CHAPTER 6 Chemical Reactions - Grygla Public School 6 Chemical Reactions ... sugar to form new substances, ... of metal alloy and begins to cor-rode the metals vigorously. Then

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C H A P T E R 6

ChemicalReactions

ChemicalReactions

1 The Nature of Chemical ReactionsChemical Reactions Change SubstancesEnergy and Reactions

2 Reaction TypesClassifying Reactions Electrons and Chemical Reactions

3 Balancing Chemical EquationsDescribing ReactionsDetermining Mole Ratios

4 Rates of ChangeFactors Affecting Reaction RatesEquilibrium Systems

Chapter Preview

Copyright © by Holt, Rinehart and Winston. All rights reserved.

Pre-Reading Questions1. When food is cooked, what are some

signs to look for to indicate that the food is ready to eat?

2. Wood is sometimes used as a fuel to provide heat and light. What other thingsin addition to wood are required to start a fire?

183

ACTIVITYACTIVITYFocusFocus

Background Many people look forward to summer as prime”grilling time.” Although there are many ways to prepare food on a grill, the basic principle is the same: raw food is cooked to make it tastier, easier to digest, and safer to eat.

One method of grilling uses charcoal as a fuel. Charcoal isproduced by heating wood or other plant matter to high temper-atures in the absence of air. When charcoal is burned on a grill,the matter in the charcoal and oxygen in the air combine in achemical reaction to produce light and heat energy that cooksthe food.

Some food can be “cooked” using chemical reactions that arenot caused by heat. For example, ceviche, which is usually servedcold, contains fish that is “cooked” with lime juice. But in allcases, when food is cooked, chemical reactions make the energyin food easier to release when you eat it.

Activity 1 Obtain three freshly cut slices of apple. Cover onecompletely with water, and wrap another slice with clear plasticwrap. Allow the third slice to remain exposed to the air. Do theslices look the same after one hour? After six hours? Why or why not?

Activity 2 Sodium bicarbonate, also known as baking soda, isused to make pancakes, cookies, and other baked goods lightand fluffy. Pour a small amount of vinegar into a cup and add apinch of baking soda to the cup. What changes do you observe?How might the same reaction cause pancakes to rise?

www.scilinks.orgTopic: Fuels SciLinks code: HK4059

The energy in charcoalis stored in chemicalbonds. When charcoalis burned, the storedenergy is released asheat and light.

Copyright © by Holt, Rinehart and Winston.All rights reserved.

The Nature of Chemical Reactions

> Recognize some signs that a chemical reaction may betaking place.

> Explain chemical changes in terms of the structure andmotion of atoms and molecules.

> Describe the differences between endothermic andexothermic reactions.

> Identify situations involving chemical energy.

If someone talks about chemical reactions, you might thinkabout scientists doing experiments in laboratories. But words

like grow, ripen, decay, and burn describe chemical reactions yousee every day. Even your own health is due to chemical reactionstaking place inside your body. The food you eat reacts with theoxygen you inhale in processes such as respiration and cellgrowth. The carbon dioxide formed in these reactions is carriedto your lungs, and you exhale it into the environment.

Chemical Reactions Change SubstancesWhen sugar, water, and yeast are mixed into flour to make breaddough, a chemical reaction takes place. The yeast acts on thesugar to form new substances, including carbon dioxide andlactic acid. You know that a chemical reaction has happenedbecause lactic acid and carbon dioxide are different from sugar.

Chemical reactions occur when substances undergo chemicalchanges to form new substances. Often you can tell that a chemi-cal reaction is happening because you will be able to see changes,such as those in Figure 1.

O B J E C T I V E S

SECTION

1

184 C H A P T E R 6

K E Y T E R M S

reactantproduct chemical energyexothermic reactionendothermic reaction

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Figure 1Signs of a Chemical Reaction

When the calcium carbonate in a piece of chalk reacts with anacid, bubbles of carbon dioxidegas are given off.

When solutions of sodium sulfide and cadmium nitrate aremixed, a solid—yellow cadmiumsulfide—settles out of the solution.

When ammonium dichromatedecomposes, energy is released as light and heat.

C

B

A

A B C


Production of gas and change of color are signs of chemical reactionsIn bread making, the carbon dioxide gas that is produced expandsthe dough, causing the bread to rise. This release of gas is a signthat a chemical reaction may be happening.

As the dough bakes, old bonds break and new bonds form.Chemical reactions involving starch and protein make food turnbrown when heated. A chemical change happens almost everytime there is a change in color.

Chemical reactions rearrange atomsWhen gasoline is burned in the engine of a car or boat, a lot ofdifferent reactions happen with the compounds that are in themixture we call gasoline. In a typical reaction, isooctane, C8H18,and oxygen, O2, are the They react and form two

carbon dioxide, CO2, and water, H2O.The products and reactants contain the same types of atoms:

carbon, hydrogen, and oxygen. New product atoms are not cre-ated, and old reactant atoms are not destroyed. Atoms arerearranged as bonds are broken and formed. In all chemical reac-tions, mass is always conserved.

Energy and ReactionsFilling a car’s tank with gasoline would be very dangerous ifisooctane and oxygen could not be in the same place withoutreacting. Like most chemical reactions, the isooctane-oxygenreaction needs energy to get started. A small spark providesenough energy to start this reac-tion. That is why smoking or hav-ing any open flame near a gaspump is not allowed.

Energy must be added to break bondsIn each isooctane molecule, likethe one shown in Figure 2, all thebonds to carbon atoms are cova-lent. In an oxygen molecule, adouble covalent bond holds thetwo oxygen atoms together. Forthe atoms in isooctane and oxygento react, all of these bonds have tobe broken. This takes energy.

products,reactants.

185

reactant a substance or molecule that participates in a chemical reaction

product a substance thatforms in a chemical reaction

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Hydrogen, HCarbon, C

Figure 2Gasoline is a mixture ofmany different compounds,each containing 5 to 12carbon atoms. Isooctane,C8H18, is representative ofthis mixture.


Reactants → ProductsIsooctane Oxygen → Carbon Water Energy

dioxide

C8H18 O2 → CO2 H2O energy

2C8H18 + 25O2 → 16CO2 + 18H2O + energy

→

Many forms of energy can be used to break bonds.Sometimes the energy is transferred as heat, like the spark thatstarts the isooctane-oxygen reaction. Energy also can be trans-ferred as electricity, sound, or light, as shown in Figure 3. Whenmolecules collide and enough energy is transferred to separatethe atoms, bonds can break.

Forming bonds releases energyOnce enough energy is added to start the isooctane-oxygen reac-tion, new bonds form to make the products, as shown in Figure 4.Each carbon dioxide molecule has two oxygen atoms connectedto the carbon atom with a double bond. A water molecule ismade when two hydrogen atoms each form a single bond withthe oxygen atom.

When new bonds form, energy is released. When gasolineburns, energy in the form of heat and light is released as the prod-ucts of the isooctane-oxygen reaction and other gasoline reactionsform. Other chemical reactions can produce electrical energy.

186 C H A P T E R 6

Figure 3Light passing through a cam-

era lens causes silver bromidecrystals on the film to form darkerelemental silver on the negative.

Light passing through the negative onto black and whitephotographic paper causesanother reaction that forms the photograph.

B

A

Figure 4The formation of carbon dioxideand water from isooctane andoxygen produces the energy usedto power engines.

NegativeA Photo (positive image)B


Energy is conserved in chemical reactionsEnergy may not appear to be conserved in the isooctane reaction.After all, a tiny spark can set off an explosion. The energy for thatexplosion comes from the bonds between atoms in the reactants.Often this stored energy is called The totalenergy of isooctane, oxygen, and their surroundings includes thischemical energy. The total energy before the reaction is equal tothe total energy of the products and their surroundings.

Reactions that release energy are exothermicIn the isooctane-oxygen reaction, more energy is released as the products form than is absorbed to break the bonds in the reactants. Like all other combustion reactions, this is an

After an exothermic reaction, the temper-ature of the surroundings rises because energy is released. Thereleased energy comes from the chemical energy of the reactants.

Reactions that absorb energy are endothermicIf you put hydrated barium hydroxide and ammonium nitratetogether in a flask, the reaction between them takes so muchenergy from the surroundings that water in the air will con-dense and then freeze on the surface of the flask. This is an

—more energy is needed to break thebonds in the reactants than is given off by forming bonds in the products.

endothermic reaction

exothermic reaction.

chemical energy.

C H E M I C A L R E A C T I O N S 187

REAL WORLDAPPLICATIONS

REAL WORLD

Self-Heating MealsCorrosion, the process by which a metal reacts with the oxygen inair or water, is not often desirable.However, corrosion is encouragedin self-heating meals so that theenergy from the exothermic reac-tion can be used. Self-heatingmeals, as the name implies, have their own heat source.

Each meal contains a packageof precooked food, a bag thatholds a porous pad containing amagnesium-iron alloy, and somesalt water. When the salt water is

chemical energy theenergy released when achemical compound reacts to produce new compounds

exothermic reaction achemical reaction in whichheat is released to the surroundings

endothermic reactiona chemical reaction thatrequires heat

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poured into the bag, the salt watersoaks through the holes in the padof metal alloy and begins to cor-rode the metals vigorously. Thenthe sealed food package is placedin the bag. The exothermic reactionraises the temperature of the foodby 38°C in 14 minutes.

Applying Information1. List some people for whom

self-heating meals would be useful.

2. What other uses can you think of for this self-heatingtechnology?

www.scilinks.orgTopic: CorrosionSciLinks code: HK4029


When an endothermic reaction occurs, you may be able tonotice a drop in temperature. Some endothermic reactions can-not get enough energy as heat from the surroundings to happen;so energy must be added as heat to cause the reaction to takeplace. The changes in chemical energy for an exothermic reac-tion and for an endothermic reaction are shown in Figure 5.

Photosynthesis, like many reactions in living things, isendothermic. In photosynthesis, plants use energy from light toconvert carbon dioxide and water to glucose and oxygen, asshown in Figure 6.

188 C H A P T E R 6

Glucose,C6H12O6

Oxygen,O2

Carbon dioxide,CO2

Water,H2O

Chem

ical

ene

rgy

Reaction

Products

Heat releasedReactants

Chem

ical

ene

rgy

Reaction

Products

Heat absorbed

Reactants

In an exothermic reaction chemi-cal energy is released, often as heat.A In an endothermic reaction,

energy from the surroundings isstored as chemical energy.

B

Figure 6All of the food you eat comesdirectly or indirectly from theproducts of photosynthesis.

Figure 5Energy must be addedto start both exothermicand endothermic reactions.

Plants Use the Energy from Light


Sometimes, reactions are described as exergonic or ender-gonic. These terms refer to the ease with which the reactionsoccur. In most cases in this book, exergonic reactions are exother-mic and endergonic reactions are endothermic. Bioluminescence,shown in Figure 7, and respiration are exergonic reactions, andphotosynthesis is an endergonic reaction.


S E C T I O N 1 R E V I E W

1. Identify which of the following is a chemical reaction:a. melting ice c. rubbing a marker on paperb. burning a candle d. rusting iron

2. List three signs that could make you think a chemical reaction might be taking place.

3. List four forms of energy that might be absorbed or releasedduring a chemical reaction.

4. Classify the following reactions as exothermic or endothermic:a. paper burning with a bright flameb. plastics becoming brittle after being left in the sunc. a firecracker exploding

5. Predict which atoms will be found in the products of the following reactions:a. mercury(II) oxide, HgO, is heated and decomposesb. limestone, CaCO3, reacts with hydrochloric acid, HClc. table sugar, C12H22O11, burns in air to form caramel

6. Critical Thinking Calcium oxide, CaO, is used in cement mixes. When water is added, heat is released as CaO forms calcium hydroxide, Ca(OH)2. What signs are there that this is a chemical reaction? Which has more chemical energy, the reactants or the products? Explain your answer.

S U M M A R Y

> During a chemical reaction,atoms are rearranged.

> Signs of a chemical reac-tion include any of the following: a substance that has different proper-ties than the reactantshave; a color change; theformation of a gas or asolid precipitate; or thetransfer of energy.

> Mass and energy are conserved in chemical reactions.

> Energy can be released or absorbed in a chemicalreaction.

> Energy must be added to the reactants for bondsbetween atoms to be broken.

BIOLOGYPeople are charmed byfireflies because thesecommon insects giveoff light. Scientists

have found that fireflies are not alone in this. Some kindsof bacteria, worms, squids, andjellyfish also give off light. Thisprocess, called biolumines-cence, involves an exothermicreaction made possible by theenzyme luciferase. Scientistscan use bacteria that containluciferase to track the spread of infection in the human body.

Some living things, suchas this firefly, produce lightthrough a chemical processcalled bioluminescence.

A The comb jelly (Mnemiopsis leidyi),shown above, is about 10 cm wideand is native to the Atlantic coast.Comb jellies are not true jellyfish.

B

Figure 7


O B J E C T I V E S

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190 C H A P T E R 6

Reaction Types> Distinguish among five general types of chemical

reactions.> Predict the products of some reactions based on the

reaction type.> Describe reactions that transfer or share electrons

between molecules, atoms, or ions.

In the last section, you saw how CO2 is made from sugar byyeast, how isooctane from gasoline burns, and how photosyn-

thesis happens. These are just a few examples of the many mil-lions of possible reactions.

Classifying ReactionsEven though there are millions of unique substances and manymillions of possible reactions, there are only a few general typesof reactions. Just as you can follow patterns to name compounds,you also can use patterns to identify the general types of chemicalreactions and to predict the products of the chemical reactions.

Synthesis reactions combine substancesPolyethene, a plastic often used to make trash bags and soda bot-tles, is produced by a called polymerization.In polymerization reactions, many small molecules join togetherin chains to make larger structures called polymers. Polyethene,shown in Figure 8, is a polymer formed of repeating ethene molecules.

Hydrogen gas reacts with oxygen gas to form water. In a syn-thesis reaction, at least two reactants join to form a product.Synthesis reactions have the following general form.

A + B → ABThe following is a synthesis reaction in which the metal sodiumreacts with chlorine gas to form sodium chloride, or table salt.

2Na + Cl2 → 2NaCl

synthesis reaction

O B J E C T I V E SK E Y T E R M S

synthesis reactiondecomposition reactionelectrolysiscombustion reactionsingle-displacement

reactiondouble-displacement

reactionoxidation-reduction

reactionradical

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Figure 8A molecule of polyethene is madeup of as many as 3500 units ofethene.

Polyethene

synthesis reaction areaction in which two ormore substances combineto form a new compound

▲

Ethene unit


Synthesis reactions always join substances, so the product is a more complex compound thanthe reactants.

Photosynthesis is another kind of synthesisreaction—the synthesis reaction that goes on in plants. The photosynthesis reaction is shown in Figure 9.

Decomposition reactions break substancesapartDigestion is a series of reactions that break downcomplex foods into simple fuels your body canuse. Similarly, in what is known as “cracking”crude oil, large molecules made of carbon andhydrogen are broken down to make gasoline andother fuels. Digestion and “cracking” oil are

reactions in whichsubstances are broken apart. The general formfor decomposition reactions is as follows.

AB → A + BThe following shows the decomposition of water.

2H2O → 2H2 + O2

The of water is a simple decom-position reaction—water breaks down into hydro-gen gas and oxygen gas when an electric currentflows through the water.

Combustion reactions use oxygen as a reactantIsooctane forms carbon dioxide and water during combustion.Oxygen is a reactant in every so at leastone product of such reactions always contains oxygen. Water is acommon product of combustion reactions.

If the air supply is limited when a carbon-containing fuelburns, there may not be enough oxygen gas for all the carbon toform carbon dioxide. In that case, some carbon monoxide mayform. Carbon monoxide, CO, is a poisonous gas that lowers theability of the blood to carry oxygen. Carbon monoxide has nocolor or odor, so you can’t tell when it is present. When there isnot a good air supply during a combustion reaction, not all fuelsare converted completely to carbon dioxide. In some combustionreactions, you can tell if the air supply is limited because theexcess carbon is given off as small particles that make a dark,sooty smoke.

combustion reaction,

electrolysis

decomposition reactions,


Figure 9Photosynthesis is the synthesis of glucose and oxy-gen gas from carbon dioxide and water.

6CO2 + 6H2O → C6H12O6 + 6O2

+ +→

decomposition reactiona reaction in which a singlecompound breaks down toform two or more simplersubstances

electrolysis the process inwhich an electric current isused to produce a chemicalreaction, such as the decom-position of water

combustion reactionthe oxidation reaction of anorganic compound, in whichheat is released

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▲

www.scilinks.orgTopic: Types of ReactionsSciLinks code: HK4142


In combustion the products depend on the amount of oxygenTo see how important a good air supply is, look at a series ofcombustion reactions for methane, CH4. Because methane hasonly one carbon atom, it is the simplest carbon-containing fuel.Methane is the primary component in natural gas, the fuel oftenused in stoves, water heaters, and furnaces.

Methane reacts with oxygen gas to make carbon dioxide andwater. In the balanced form of the chemical equation, four mol-ecules of oxygen gas are needed for the combustion of two mol-ecules of methane, as shown below.

2CH4�4O2 → 2CO2�4H2O

Now look at what happens when less oxygen gas is available. Ifthere are only three molecules of oxygen gas for every two mol-ecules of methane, water and carbon monoxide may form, asshown in the following reaction.

2CH4�3O2 → 2CO � 4H2O

When the air supply is very limited and only two molecules ofoxygen gas are available to react with two molecules of methane,water and tiny bits of carbon, or soot, are formed as follows.

2CH4�2O2 → 2C � 4H2O

192 C H A P T E R 6

++

++

++

In the United States, naturalgas supplies one-fifth of theenergy used. The pipelinesthat carry this natural gas, iflaid end-to-end, would stretchto the moon and back twice.

EARTH SCIENCECompounds containingcarbon and hydrogenare often called hydro-carbons. Most hydro-

carbon fuels are fossil fuels, that is, compounds that wereformed millions of yearsbefore dinosaurs existed.When prehistoric organismsdied, they decomposed, andmany were slowly buriedunder layers of mud, rock, andsand. During the millions ofyears that passed, the once-living material formed differ-ent fuels, such as oil, naturalgas, or coal, depending on thekind of material present, thelength of time the materialwas buried, and the condi-tions of temperature and pres-sure that existed when thematerial was decomposing.


A fire is a combustion reaction in progress thatis speeded up by high temperatures. Threethings are needed for a combustion reaction

to occur: a fuel, some oxygen, and an ignitionsource. If any of these three is absent, combustioncannot occur. So the goal of firefighting is to removeone or more of these parts. Fire extinguishers areeffective in firefighting because they separate the fuelfrom the oxygen supply, which is most commonly air.

Classes of FiresA fire is classified by the type of fuel that combuststo produce it. Class A fires involve solid fuels, such aswood and paper. The fuel in a Class B fire is a flam-mable liquid, like grease, gasoline, or oil. Class C firesinvolve “live” electric circuits. And Class D fires are fueled by the combustion of flammable metals.

Types of Fire ExtinguishersDifferent types of fuels require different firefightingmethods. Water extinguishers are used on Class Afires, which involve fuels such as most flammablebuilding materials. The steam that is produced helpsto displace the air around the fire, preventing theoxygen supply from reaching the fuel.

A Class B fire, in which the fuel is a liquid, is bestput out by cold carbon dioxide gas, CO2. Becausecarbon dioxide is more dense than air, it forms alayer underneath the air, cutting off the oxygen sup-ply for the combustion reaction.

Class C fires, which involve a “live” electric circuit,can also be extinguished by CO2. Liquid water cannotbe used, or there will be a danger of electric shock.Some Class C fire extinguishers contain a dry chemi-cal that smothers the fire. The dry chemical smothersthe fire by reacting with the intermediates that drivethe chain reaction that produces the fire. This stopsthe chain reaction and extinguishes the fire.

Finally, Class D fires, which involve burning metals,cannot be extinguished with CO2 or water becausethese compounds may react with some hot metals.For these fires, nonreactive dry powders are used tocover the metal and keep it separate from oxygen. Inmany cases, the powders used in Class D exting-uishers are specific to the type of metal that is burning.

Most fire extinguishers can be used with morethan one type of fire. Check the fire extinguishers inyour home and school to find out the kinds of firesthey are designed to put out.

1. Making Decisions Aside from displacing theair supply, how does water or cold CO2 gasreduce a fire’s severity?

2. Critical Thinking How is the chain reaction ina Class C fire interrupted by the contents of adry chemical extinguisher?

Your Choice

Fire extinguishersdisplay codes indicating whichtypes of fires theycan put out.

and the Consumerand the ConsumerScienceScience

Fire Extinguishers: Are They All The Same?


www.scilinks.orgTopic: Fire Extinguishers SciLinks code: HK4052


In single-displacement reactions, elements trade placesCopper(II) chloride dissolves in water to make a bright blue solu-tion. If you add a piece of aluminum foil to the solution, the colorfades, and clumps of reddish brown material form. The reddishbrown clumps are copper metal. Aluminum replaces copper inthe copper(II) chloride, forming aluminum chloride. Aluminumchloride does not make a colored solution, so the blue color fadesas the amount of blue copper(II) chloride decreases, as shown inFigure 10.

At first, the copper atoms are in the form of copper(II) ions,as part of copper(II) chloride, and the aluminum atoms are in theform of aluminum metal. After the reaction, the aluminumatoms become ions, and the copper atoms become neutral in thecopper metal. Because the atoms of one element appear to moveinto a compound, and atoms of the other element appear to moveout, this is called a Single-displacement reactions have the following general form.

AX + B → BX + AThe single-displacement reaction between copper(II) chlorideand aluminum is shown as follows.

3CuCl2 + 2Al → 2AlCl3 + 3CuGenerally, in a single-displacement reaction, a more reactive el-ement will take the place of a less reactive one.

single-displacement reaction.

194 C H A P T E R 6

Figure 10Aluminum undergoes asingle-displacement reac-tion with copper(II) chlo-ride to form copper andaluminum chloride.

→

→

3CuCl2 + 2Al → 2AlCl3 + 3Cu

Copper atom

Aluminum ion, Al3+

Aluminum atom

Copper ion, Cu2+

Chloride ion, Cl–

Water molecule

single-displacementreaction a reaction in whichone element or radical takesthe place of another elementor radical in a compound

▲


Alkali metals react with water to form ionsPotassium metal is so reactive that it undergoes a single-displacement reaction with water. A potassium ion appears totake the place of one of the hydrogen atoms in the water mol-ecule. Potassium ions, K+, and hydroxide ions, OH–, are formed.The hydrogen atoms displaced from the water join to formhydrogen gas, H2.

The potassium and water reaction, shown in Figure 11, is soexothermic that the H2 may explode and burn instantly. All alkalimetals and some other metals undergo single-displacement reac-tions with water to form hydrogen gas, metal ions, and hydrox-ide ions.

All of these reactions happen rapidly and give off heat butsome alkali metals are more reactive than others. Lithium reactssteadily with water to form lithium ions, hydroxide ions, andhydrogen gas. Sodium and water react vigorously to makesodium ions, hydroxide ions, and hydrogen gas. Rubidium andcesium are so reactive that the hydrogen gas will explode as soonas they are put into water.

In double-displacement reactions, ions appear to beexchanged between compoundsThe yellow lines painted on roads are colored with lead chro-mate, PbCrO4. This compound can be formed by mixing solu-tions of lead nitrate, Pb(NO3)2, and potassium chromate,K2CrO4. In solution, these compounds form the ions Pb2�, NO3

�,K�, and CrO2

4–. When the solutions are mixed, the yellow lead

chromate compound that forms doesn’t dissolve in water, so itsettles to the bottom. A such asthis one, occurs when two compounds appear to exchange ions.The general form of a double-displacement reaction is as follows.

AX + BY → AY + BXThe double-displacement reaction that forms lead chromate is asfollows.

Pb(NO3)2 + K2CrO4 → PbCrO4 + 2KNO3

double-displacement reaction,


Potassium,K

Water,H2O

Potassium hydroxide,KOH

Hydrogen,H2

++

Figure 11Potassium reacts with water in asingle-displacement reaction.

→

double-displacementreaction a reaction in which a gas, a solid precipitate, or amolecular compound formsfrom the apparent exchangeof atoms or ions between two compounds

▲


Electrons and Chemical ReactionsThe general classes of reactions described earlier in this sectionwere used by early chemists, who knew nothing about the parts ofthe atom. With the discovery of the electron and its role in chemi-cal bonding, another way to classify reactions was developed. Wecan understand many reactions as transfers of electrons.

Electrons are transferred in redox reactionsThe following is an example ofelectron transfer. When the metal iron reacts with oxygen to formrust, Fe2O3, each iron atom loses three electrons to form Fe3� ions, and each oxygen atom gains two electrons to form theO2– ions.

Substances that accept electrons are said to be reduced; sub-stances that give up electrons are said to be oxidized. One way toremember this is that the gain of electrons will reduce the posi-tive charge on an ion or will make an uncharged atom a negativeion. Reduction and oxidation are linked. In all redox reactions,one or more reactants is reduced and one or more is oxidized.

Some redox reactions do not involve ions. Inthese reactions, oxidation is a gain of oxygen or aloss of hydrogen, and reduction is the loss of oxy-gen or the gain of hydrogen. Respiration and com-bustion are redox reactions because oxygen gasreacts with carbon compounds to form carbondioxide. Carbon atoms in CO2 are oxidized, andoxygen atoms in O2 are reduced.

Radicals have electrons available for bondingMany synthetic fibers, as well as plastic bags andwraps, are made by polymerization reactions, asyou have already learned. Polymerization reac-tions can occur when are formed.

When a covalent bond is broken such that atleast one unpaired electron is left on each frag-ment of the molecule, these fragments are calledradicals. Because an uncharged hydrogen atomhas one electron available for bonding, it is a radi-cal. Radicals react quickly to form covalent bondswith other substances, making new compounds.Often, when you see chemical radicals mentionedin the newspaper or hear about them on the radioor television, they are called free radicals.

radicals

oxidation-reduction reaction

196 C H A P T E R 6

Connection toFINE ARTSFINE ARTS

Metal sculptures often cor-rode because of redox

reactions. The Statue ofLiberty, which is coveredwith 200 000 pounds ofcopper, was as bright as anew penny when it waserected. However, after morethan 100 years, the statue hadturned green. The copper reacted with the dampair of New York harbor. More importantly, oxida-tion reactions between the damp, salty air andthe internal iron supports made the structuredangerously weak. The statue was closed forseveral years in the 1980s while the supportswere cleaned and repaired.

Making the Connection1. Metal artwork in fountains often rusts very

quickly. Suggest a reason for this.

2. Why do you think the most detailed parts ofa sculpture are the first to appear worn away?

oxidation-reductionreaction any chemicalchange in which one speciesis oxidized (loses electrons)and another species isreduced (gains electrons);also called redox reaction

radical an organic groupthat has one or more elec-trons available for bonding

▲▲




1. Classify each of the following reactions by type:a. S8 � 8O2 → 8SO2 � heatb. 6CO2 � 6H2O → C6H12O6 � 6O2

c. 2NaHCO3 → Na2CO3 � H2O � CO2

d. Zn � 2HCl → ZnCl2 � H2

2. Identify which element is oxidized and which element isreduced in the following reaction.

Zn � CuSO4 → ZnSO4 � Cu

3. Define radical.

4. Compare and Contrast single-displacement and double-displacement reactions based on the number of reactants.Use the terms compound, atom or element, and ion.

5. Explain why charcoal grills or charcoal fires should never be used for heating inside a house. (Hint: Doors and win-dows are closed when it is cold, so there is little fresh air.)

6. Contrast synthesis and decomposition reactions.

7. List three possible results of a double-displacement reaction.

8. Creative Thinking Would you expect larger or smaller mol-ecules to be components of a more viscous liquid? Which islikely to be more viscous, crude oil or oil after cracking?

S U M M A R Y

> Synthesis reactions makelarger molecules.

> Decomposition breakscompounds apart.

> In combustion, substancesreact with oxygen.

> Elements appear to trade places in single-displacement reactions.

> In double-displacementreactions, ions appear tomove between compounds,resulting in a solid that set-tles out of solution, a gasthat bubbles out of solu-tion, and/or a molecularsubstance.

> In redox reactions, elec-trons transfer from onesubstance to another.

Radicals are part of many everyday reactions besides themaking of polymers, such as those shown in Figure 12. Radicalscan also be formed when coal and oil are processed or burned.The explosive combustion of rocket fuel is another reactioninvolving the formation of radicals.

Figure 12Radical reactions are used tomake polystyrene. Polystyrenefoam is often used to insulate orto protect things that can break.


Balancing Chemical Equations> Demonstrate how to balance chemical equations.> Interpret chemical equations to determine the relative

number of moles of reactants needed and moles ofproducts formed.

> Explain how the law of definite proportions allows forpredictions about reaction amounts.

> Identify mole ratios in a balanced chemical equation.> Calculate the relative masses of reactants and products

from a chemical equation.

You may have seen a combustion reaction in the lab or athome if you have a gas stove. When natural gas burns,

methane, the main component, reacts with oxygen gas to formcarbon dioxide and water. Energy is also released as heat andlight, as shown in Figure 13A.

Describing ReactionsYou can describe this reaction in many ways. You could take aphotograph or make a videotape. One way to record the productsand reactants of this reaction is to write a word equation.

methane + oxygen → carbon dioxide + water

Chemical equations summarize reactionsIn Section 1, you learned that all chemical reactions are re-arrangements of atoms. This is shown clearly in Figure 13B. Abetter way to write the methane combustion reaction is as a

using the formulas for each substance.chemical equation,

O B J E C T I V E S

SECTION

3

K E Y T E R M S

chemical equationmole ratio

▲

Figure 13

Methane burns with oxygen gas to makecarbon dioxide and water.BA methane flame is used to

polish the edges of these glassplates.

A

Methane, CH4

Oxygen,O2

Carbon dioxide,CO2

Water,H2O

chemical equation a rep-resentation of a chemicalreaction that uses symbols to show the relationshipbetween the reactants and the products

▲

198 C H A P T E R 6

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In a chemical equation, such as the one above, the reactants,which are on the left-hand side of the arrow, form the products,which are on the right-hand side. When chemical equations arewritten, → means “gives” or “yields.” People all over the worldwrite chemical equations the same way, as shown in Figure 14.

Balanced chemical equations account for the conservationof massThe chemical equation shown above can be made more useful.As written, it does not tell you anything about the amount of theproducts that will be formed from burning a given amount ofmethane. When the number of atoms of each element on theright-hand side of the equation matches the number of atoms ofeach element on the left, then the chemical equation is said to bebalanced. A balanced chemical equation is the standard way ofwriting equations for chemical reactions because it follows thelaw of conservation of mass.

How to balance chemical equationsIn the previous equation, the number of atoms on each side ofthe arrow did not match for all of the elements in the equation.Carbon is balanced because one carbon atom is on each side ofthe equation. However, four hydrogen atoms are on the left, andonly two are on the right. Also, two oxygen atoms are on the left,and three are on the right. This can’t be correct because atomscan’t be created or destroyed in a chemical reaction.

Remember that you cannot balance an equation by changingthe chemical formulas. You have to leave the subscripts in theformulas alone. Changing the formulas would mean that differ-ent substances were in the reaction. An equation can be balancedonly by putting numbers, called coefficients, in front of thechemical formulas.

Because there is a total of four hydrogen atoms in the react-ants, a total of four hydrogen atoms must be in the products.Instead of a single water molecule, this reaction makes two watermolecules to account for all four hydrogen atoms. To show thattwo water molecules are formed, a coefficient of 2 is placed infront of the formula for water.

CH4 � O2 → CO2 � 2H2O


CH4 + O2 → CO2 + H2O

Unbalanced Chemical Equation

Figure 14This student is giving a talk on reactions that use copper. You can read the chemical equationseven if you can’t read Japanese.

reactants “give” or “yield” products


Next look at the oxygen. There is a total of fouroxygen atoms in the products. Two are in the CO2,and each water molecule contains one oxygenatom. To get four oxygen atoms on the left side ofthe equation, two oxygen molecules must react.That would account for all four oxygen atoms.

Now the numbers of atoms for each element arethe same on each side, and the equation is bal-anced, as shown below.

Information from a balanced equationYou can learn a lot from a balanced equation. In our example,you can tell that each molecule of methane requires two oxygenmolecules to react. Each methane molecule that burns forms onemolecule of carbon dioxide and two molecules of water.Balanced chemical equations are the standard way chemistswrite about reactions to describe both the substances in the reac-tion and the amounts involved.

If you know the formulas of the reactants and products in areaction, like the one shown in Figure 15, you can always write abalanced equation, as shown on the following pages.

200 C H A P T E R 6

Figure 15Magnesium in these fireworksgives off energy as heat and light when it burns to form magnesium oxide.

Connection toSOCIAL STUDIESSOCIAL STUDIES

No one can be sure when fireworks were first used. When the Mongols attacked

China in 1232, the defenders used “arrows offlying fire,” which some historians think wererockets fired by gunpowder. The Arabs probablyused rockets when they invaded the Spanishpeninsula in 1249. For hundreds of years, themain use of rockets was to add terror and con-fusion to battles. In the late 1700s, rockets wereused with some success against the British inIndia. Because of this, Sir William Congrevebegan to design rockets for England. Congreve’srockets were designed to explode in the air orbe fired along the ground.

Making the ConnectionBritish forces used Congreve’s rockets during the War of 1812. Research the battle of FortMcHenry. Find out what happened, who wonthe battle, and what lyrics the rockets inspired.

CH4�2O2 → CO2�2H2O

Balanced Chemical Equation

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Disc One, Module 5:Chemical EquationsUse the Interactive Tutor to learn moreabout this topic.

→

Copyright © by Holt, Rinehart and Winston.All rights reserved.


PracticeHINT

> Sometimes changing the coefficients to balance one element may cause anotherelement in the equation to become unbalanced. So always check your work.

Math SkillsMath Skills

Balancing Chemical Equations Write the equation that describes the burning of magnesium in air to form magnesium oxide.

Identify the reactants and products.Magnesium and oxygen gas are the reactants that formthe product, magnesium oxide.

Write a word equation for the reaction.

magnesium � oxygen → magnesium oxide

Write the equation using formulas for the elements andcompounds in the word equation.

Remember that some gaseous elements, like oxygen,are molecules, not atoms. Oxygen in air is O2, not O.

Mg � O2 → MgO

Balance the equation one element at a time.The same number of each kind of atom must appear onboth sides. So far, there is one atom of magnesium oneach side of the equation.

Atom Reactants Products Balanced?

Mg 1 1 ✔

O 2 1 ✘

But there are two oxygen atoms on the left and only oneon the right. To balance the number of oxygen atoms,you need to double the amount of magnesium oxide:

Mg � O2 → 2MgO


Mg 1 2 ✘

O 2 2 ✔

This equation gives you two magnesium atoms on theright and only one on the left. So you need to double theamount of magnesium on the left, as follows.

2Mg � O2 → 2MgO


Mg 2 2 ✔

O 2 2 ✔

Now the equation is balanced. It has an equal numberof each type of atom on both sides.

4

3

2

1


Determining Mole RatiosLook at the reaction of magnesium with oxygen to form magne-sium oxide.

magnesium � oxygen → magnesium oxide

2Mg � O2 → 2MgO

The single molecule of oxygen in the equation might be shown as102. However, a coefficient of 1 is never written.

Balanced equations show the conservation of massOther ways of looking at the amounts in the reaction are shownin Figure 16. Notice that there are equal numbers of magnesiumand oxygen atoms in the product and in the reactants. The totalmass of the reactants is always the same as the total mass of theproducts.

202 C H A P T E R 6

PracticePracticeBalancing Chemical Equations1. Copper(II) sulfate, CuSO4, and aluminum react to form

aluminum sulfate, Al2(SO4)3, and copper. Write the balancedequation for this single-displacement reaction.

2. In a double-displacement reaction, sodium sulfide, Na2S, reactswith silver nitrate, AgNO3, to form sodium nitrate, NaNO3, and silver sulfide, Ag2S. Balance this equation.

3. Hydrogen peroxide, H2O2, is sometimes used as a bleach or as a disinfectant. Hydrogen peroxide decomposes to give water and molecular oxygen. Write a balanced equation for the decomposition reaction.

Figure 16 Information from the Balanced Equation: 2Mg � O2 → 2MgO

Equation: 2Mg � O2 → 2MgO

Amount (mol) 2 1 → 2

Molecules (6.02 � 1023) × 2 (6.02 � 1023) � 1 → (6.02 × 1023) × 2

Mass (g) 24.3 g/mol � 2 mol 32.0 g/mol � 1 mol → 40.3 g/mol × 2 mol

Total mass (g) 48.6 32.0 → 80.6

Model →


The law of definite proportionsWhat if you want 4 mol of magnesium to react completely? If youhave twice as much magnesium as the balanced equation callsfor, you will need twice as much oxygen. Twice as much magne-sium oxide will be formed. No matter what amounts of magne-sium and oxygen are combined or how the magnesium oxide ismade, the balanced equation does not change. This follows thelaw of definite proportions, which states:

A compound always contains the same elements in the same proportions, regardless of how the compound is made or

how much of the compound is formed.

Mole ratios can be derived from balanced equationsWhether the magnesium-oxygen reaction starts with 2 mol or 4 mol of magnesium, the proportions remain the same. One wayto understand this is to look at the from the bal-anced equation. For 2 mol of magnesium and 1 mol of oxygen,the ratio is 2:1. If 4 mol of magnesium is present, 2 mol of oxy-gen is needed to react. The ratio is 4:2, which reduces to 2:1.

The mole ratio for any reaction comes from the balancedchemical equation. For example, in the following equation forthe electrolysis of water, the mole ratio for H2O:H2:O2, using thecoefficients, is 2:2:1.

2H2O → 2H2 + O2

As you can see in Figure 17, the hydrogen gas produced oc-cupies twice the volume of the oxygen gas. That is because thereare twice as many molecules of hydrogen gas produced in elec-trolysis as there are molecules of oxygen gas.

Mole ratios allow you to calculate the mass of the reactants If you know the mole ratios of the substances involved in a reac-tion, you can determine the relative masses of the substancesrequired to react completely.

The most convenient way to determine the relative masses isby multiplying the molecular mass of each substance by the moleratio from the balanced equation. For example, for the reactionshown in Figure 16, the atomic mass of magnesium, 24.3 g/mol,is multiplied by 2 to get a total mass of 48.6 g. The mass of mo-lecular oxygen, 32.0 g/mol, is multiplied by 1. This means that inorder for magnesium to react completely with oxygen, theremust be 32 g of oxygen available for every 48.6 g of magnesium.

mole ratios


Figure 17 Electrical energy causes thedecomposition of water into oxy-gen (in the test tube on the left)and hydrogen (on the right).

mole ratio the relativenumber of moles of the sub-stances required to produce a given amount of product ina chemical reaction

▲


204 C H A P T E R 6


1. Identify which of the following is a complete and balancedchemical equation:a. H2O → H2 � O2 c. Fe � S → FeSb. NaCl + H2O d. CaCO3

2. Balance the following equations:a. KOH � HCl → KCl � H2Ob. Pb(NO3)2 � KI → KNO3 � PbI2

c. NaHCO3 → H2O + CO2 + Na2CO3

d. NaCl � H2SO4 → Na2SO4 � HCl

3. Explain why the numbers in front of chemical formulas, notthe subscripts, must be changed to balance an equation.

4. Describe the information needed to calculate the mass of areactant or product for the following balanced equation:

FeS � 2HCl → H2S � FeCl2

5. Critical Thinking Ammonia is manufactured by the Haberprocess in the reaction shown below:

N2�3H2→← 2NH3�heat

This involves the reaction of nitrogen with hydrogen. Whatmass of nitrogen is needed to make 34 g of ammonia?

S U M M A R Y

> A chemical equation showsthe reactants that combineand the products that resultfrom the reaction.

> Balanced chemical equa-tions show the proportionsof reactants and productsneeded for the mass to beconserved.

> A compound always con-tains the same elements in the same proportions, regardless of how the com-pound is made or howmuch of the compound isformed.

> A mole ratio relates theamounts of any two ormore substances involvedin a chemical reaction.

Materials

Can you determine the products of a reaction?

✔ 7 test tubes ✔ test-tube rack ✔ labels or wax pencil ✔10 mL graduated cylinder✔ bottles of the following solutions: sodium chloride, NaCl; potassium bromide, KBr;

potassium iodide, KI; and silver nitrate, AgNO3

SAFETY CAUTION Wear safety goggles and anapron. Silver nitrate will stain your skin and clothes.

1. Label three test tubes, one each for NaCl, KBr,and KI.

2. Using the graduated cylinder, measure 5 mL ofeach solution into the properly labeled test tube.Rinse the graduated cylinder between each use.

3. Add 1 mL of AgNO3 solution to each of the testtubes. Record your observations.

Analysis1. What did you observe as a sign that a double-

displacement reaction was occurring?

2. Identify the reactants and products for each reaction.

3. Write the balanced equation for each reaction.

4. Which ion(s) produced a solid with silver nitrate?

5. Does this test let you identify all the ions? Why or why not?


> Describe the factors affecting reaction rates.> Explain the effect a catalyst has on a chemical reaction.> Explain chemical equilibrium in terms of equal forward

and reverse reaction rates.> Apply Le Châtelier’s principle to predict the effect of

changes in concentration, temperature, and pressure inan equilibrium process.

Rates of Change

Chemical reactions can occur at different speeds or rates.Some reactions, such as the explosion of nitroglycerin,

shown in Figure 18, are very fast. Other reactions, such as theburning of carbon in charcoal, are much slower. But what if youwanted to slow down the nitroglycerin reaction to make it safer?What if you wanted to speed up the reaction by which yeast makecarbon dioxide, so bread would rise in less time? If you thinkcarefully, you may already know some things about how tochange reaction rates.

Factors Affecting Reaction RatesThink about the following observations:

> A potato slice takes 5 minutes to fry in oil at200°C but takes 10 minutes to cook in boilingwater at 100°C. Therefore, potatoes cookfaster at higher temperatures.

> Potato slices take 10 minutes to cook in boil-ing water, but whole potatoes take about30 minutes to boil. Therefore, potatoes cookfaster if you cut them up into smaller pieces.

These observations relate to the speed of chemi-cal reactions. For any reaction to occur, the parti-cles of the reactants must collide with oneanother. In each situation where the potatoescooked faster, the contact between particles wasgreater, so the cooking reaction went faster.

O B J E C T I V E S

SECTION

4


K E Y T E R M S

catalystenzymesubstrate chemical equilibrium

▲

Figure 18Nitroglycerin can be used as arocket fuel as well as a medicinefor people with heart ailments.

OxygenCarbon

Nitrogen

Hydrogen

www.scilinks.orgTopic: Factors Affecting

Reaction RateSciLinks code: HK4051


Figure 19Mold will grow on bread

stored at room temperature.Bread stored in the freezer

for the same length of timewill be free of mold when youtake it out.

B

A

Figure 20When a solid is divided intopieces, the total surface areabecomes larger.

206 C H A P T E R 6

A B

Most reactions go faster at higher temperaturesHeating food speeds up the chemical reactions that happen incooking. Cooling food slows down the chemical reactions thatresult in spoiling, as shown in Figure 19.

The kinetic theory states that particles move faster at highertemperatures. The faster moving particles collide more often, andthere are more chances for the particles to react. Therefore, thereaction will be faster.

A large surface area speeds up reactionsWhen a whole potato is placed in boiling water, only the outsideis in direct contact with the boiling water. The energy transferredfrom the water takes longer to reach the center of the potato thanit would if the potato were sliced. As Figure 20 shows, cuttingpotatoes into pieces allows parts that were inside the potato to beexposed. In other words, the surface area of the potato isincreased. The surface area of a solid is the amount of the surfacethat is exposed. Generally solids that have a large surface areareact more rapidly because more particles can come in contactwith the other reactants.

Concentrated solutions react fasterThink about a washing machine full of clothes withgrass stains on them. If you put a drop of bleach in thewater, little will happen to the dirty clothes. If you poura bottle of bleach into the washing machine, the stainedclothes will be clean. The more concentrated solutionhas more bleach particles. This means a higher chancefor particle collisions with the stains.

Reactions are faster at higher pressureThe concentration of a gas can be thought of asthe number of particles in a given volume. A gasat high pressure is more concentrated than thesame amount of a gas at a low pressure becausethe gas at high pressure has been squeezed intoa smaller volume. Gases react faster at higherpressures; the particles have less space, so theyhave more collisions.


Massive, bulky molecules react slowerThe size and shape of the reactant molecules affect the rate ofreaction. You know from the kinetic theory of matter that mas-sive molecules move more slowly than less massive molecules atthe same temperature. This means that for equal numbers ofmassive and “light” molecules of about the same size, the mol-ecules with more mass collide less often with other molecules.

Some molecules, such as large biological compounds, mustfit together in a particular way to react. They can collide withother reactants many times, but if the collision occurs on thewrong end of the molecule, they will not react. Generally thesecompounds react very slowly because many unsuccessful colli-sions may occur before a successful collision begins the reaction.

Catalysts change the rates of chemical reactionsWhy add a substance to a reaction if the substance may notreact? This is done all the time in industry when areadded to make reactions go faster. Catalysts are not reactants orproducts. They speed up or slow reactions. Catalysts that slowreactions are called inhibitors. Catalysts are used to help makeammonia, to process crude oil, and to accelerate making plastics.Catalysts can be expensive and still be profitable because theycan be cleaned or renewed and reused. Sometimes the name ofthe catalyst is written over the reaction arrow of a chemical equa-tion when a catalyst is present.

Catalysts work in different ways. Most solid catalysts, such asthose in car exhaust systems, speed up reactions by providing asurface where the reactants can collect and react. Then the reac-tants can form new bonds to make the products. Most solid cat-alysts are more effective if they have a large surface area.

Enzymes are biological catalystsare proteins that are

catalysts for chemical reactions inliving things. Enzymes are veryspecific. Each enzyme controls onereaction or set of similar reactions.Some common enzymes and thereactions they control are listed inTable 1. Most enzymes are fragile. Ifthey are kept too cold or too warm,they tend to decompose. Mostenzymes stop working above 45°C.

Enzymes

catalysts


catalyst a substance thatchanges the rate of a chemicalreaction without being con-sumed or changed significantly

enzyme a type of proteinthat speeds up metabolicreactions in plants and ani-mals without being perma-nently changed or destroyed

▲▲

Enzyme Substrate What the enzyme does

Amylase starch breaks down long starch molecules into sugars

Cellulase cellulose breaks down long cellulose molecules into sugars

DNA nucleic acid builds up DNA chains in polymerase cell nuclei

Lipase fat breaks down fat into smaller molecules

Protease protein breaks down proteins into amino acids

Table 1 Common Enzymes and Their Uses

www.scilinks.orgTopic: CatalystsSciLinks code: HK4018


Catalase, an enzyme produced by humans and most other liv-ing organisms, breaks down hydrogen peroxide. Hydrogen per-oxide is the for catalase.

2H2O2 2H2O + O2

For an enzyme to catalyze a reaction, the substrate and theenzyme must fit exactly—like a key in a lock. This fit is shown inFigure 21. Enzymes are very efficient. In 1 minute, one moleculeof catalase can catalyze the decomposition of 6 million moleculesof hydrogen peroxide.

catalase→

substrate

208 C H A P T E R 6

Materials

What affects the rates of chemical reactions?

✔ Bunsen burner ✔ sandpaper ✔ steel wool ball, ✔ magnesium ribbon,✔ paper clip ✔ tongs 2 cm diameter copper foil strip,✔ 6 test tubes ✔ matches ✔ graduated cylinder zinc strip; each 3 cm ✔ paper ash ✔ 2 sugar cubes ✔ vinegar long, uniform width

SAFETY CAUTION Wear safety goggles and anapron. 1. Label three test tubes 1, 2, and 3. Place 10 mL of

vinegar in each test tube. Sandpaper the metalsuntil they are shiny. Then add the magnesium to test tube 1, the zinc to test tube 2, and thecopper to test tube 3. Record your observations.

2. Using tongs, hold a paper clip in the hottest partof the burner flame for 30 s. Repeat with a ballof steel wool. Record your observations.

3. Label three more test tubes A, B, and C. To testtube A, add 10 mL of vinegar; to test tube B, add

5 mL of vinegar and 5 mL of water; and to testtube C, add 2.5 mL of vinegar and 7.5 mL ofwater. Add a piece of magnesium ribbon toeach test tube. Record your observations.

4. Using tongs, hold a sugar cube and try to igniteit with a match. Rub paper ash on another cube and try again. Record your observations.

Analysis

1. Describe and interpret your results.

2. For each step, list the factor(s) that influencedthe rate of reaction.

Figure 21The enzyme hexokinase catalyzesthe addition of phosphate to glu-cose. This model shows theenzyme, in blue, before andafter it fits with a glucose mol-ecule, shown in red.

B

A

substrate a part, substance,or element that lies beneathand supports another part,substance, or element; thereactant in reactions catalyzedby enzymes

▲

A B


Equilibrium SystemsWhen nitroglycerin explodes, not much nitroglycerin is left. Whenan iron nail rusts, given enough time, all the iron is converted toiron(III) oxide and only the rust remains. Even though an explo-sion occurs rapidly and rusting occurs slowly, both reactions go tocompletion. Most of the reactants are converted to products, andthe amount that is not converted is not noticeable and usually isnot important.

Some changes are reversibleYou may get the idea that all chemical reactions go to completionif you watch a piece of wood burn or see an explosion. However,reactions don’t always go to completion; some are reversible.

For example, carbonated drinks, such as the soda shown inFigure 22, contain carbon dioxide. These drinks are manufac-tured by dissolving carbon dioxide in water under pressure. Tokeep the carbon dioxide dissolved, you need to maintain the pres-sure by keeping the top on the bottle. Opening the soda allowsthe pressure to decrease. When this happens, some of the carbondioxide comes out of solution, and you see a stream of carbondioxide bubbles. This carbon dioxide change is reversible.

CO2 (gas above liquid) CO2 (gas dissolved in liquid)

The reaction can go in either direction. The →← sign indicates areversible change. Compare it with the arrow you normally see inchemical reactions, →, which indicates a change that goes inone direction—toward completion.

increase pressure

←→decrease pressure


ACTIVITYACTIVITYQuickQuickQuick

A bottle of carbonatedwater with the top on is atequilibrium.

A When the top is removed,the carbonated water is nolonger at equilibrium.

B

Figure 22

Catalysts in Action1. Pour 2% hydrogen

peroxide into a test tubeto a depth of 2 cm.

2. Pour 2 cm of water intoanother test tube.

3. Drop a small piece ofraw liver into each testtube.

4. Liver contains theenzyme catalase. Watchcarefully, and describewhat happens. Explainyour observations.

5. Repeat steps 1–4 usinga piece of liver that hasbeen boiled for 3 min-utes. Explain your result.

6. Repeat steps 1–4 againusing iron filings insteadof liver. What happens?


Equilibrium results when rates balanceWhen a carbonated drink is in a closed bottle, you can’t see anychanges. The system is in —a balancedstate. This balanced state is dynamic. No changes are apparent,but changes are occurring. If you could see individual moleculesin the bottle, you would see continual change. Molecules of CO2

are coming out of solution constantly. However, CO2 moleculesfrom the air above the liquid are dissolving at the same time andthe same rate.

The result is that the amount of dissolved and undissolvedCO2 doesn’t change, even though individual CO2 molecules aremoving in and out of the solution. This is similar to the numberof players on the field for a football team. Although differentplayers can be on the field at any time, eleven players are alwayson the field for each team.

Systems in equilibrium respond to minimize changeWhen the top is removed from a carbonated drink, the drink isno longer at equilibrium, and CO2 leaves as bubbles. For equilib-rium to be reached, none of the reactants or products can escape.

The conversion of limestone, CaCO3, to lime, CaO, is a chemi-cal reaction that can lead to equilibrium. Limestone and sea-shells, which are also made of CaCO3, were used to make limemore than 2000 years ago. By heating limestone in an open pot,lime was produced to make cement. The ancient buildings inGreece and Rome, such as the one shown in Figure 23, were prob-ably built with cement made by this reaction.

CaCO3 � heat → CaO � CO2

Because the CO2 gas can escape from an openpot, the reaction proceeds until all of the limestoneis converted to lime.

However, if some dry limestone is sealed in aclosed container and heated, the result is different.As soon as some CO2 builds up in the container, thereverse reaction starts. Once the concentrations ofthe CaCO3, CaO, and CO2 stabilize, equilibrium isestablished.

CaCO3→← CaO � CO2

If there aren’t any changes in the pressure or thetemperature, the forward and reverse reactions con-tinue to take place at the same rate. The concentra-tion of CO2 and the amounts of CaCO3 and CaO inthe container do not change.

chemical equilibrium

Equilibrium comes from theLatin aequilibris meaningequally balanced. In Latin,aequil means equal, and librameans a balance scale. You may have seen the constellationcalled Libra. The stars in theconstellation roughly represent a balance.

V

chemical equilibriuma state of balance in whichthe rate of a forward reactionequals the rate of the reversereaction and the concentra-tions of products and reac-tants remain unchanged

▲

Figure 23Cement for ancient buildings,like this one in Limeni, Greece,probably contained lime madefrom seashells.


Le Châtelier’s principle predicts changes in equilibriumLe Châtelier’s principle is a general rule that describes the behav-ior of equilibrium systems.

If a change is made to a system in chemical equilibrium,the equilibrium shifts to oppose the change

until a new equilibrium is reached.

The effects of different changes on an equilibrium system areshown in Table 2.

Ammonia is a chemical building block used to make fertil-izers, dyes, plastics, cosmetics, cleaning products, and fire retar-dants, such as those you see being applied in Figure 24. TheHaber process, which is used to make ammonia industrially, isexothermic; it releases energy.

nitrogen + hydrogen →← ammonia + heat

N2 (gas) + 3H2 (gas) →← 2NH3 (gas) + heat

At an ammonia-manufacturing plant production chemists mustchoose the conditions that favor the highest yield of NH3. Inother words, the equilibrium should favor the productionof NH3.

Table 2 The Effects of Change on Equilibrium

Temperature Increasing temperature favors the reaction thatabsorbs energy.

Pressure Increasing pressure favors the reaction that produces fewer molecules of gas.

Concentration Increasing the concentration of one substancefavors the reaction that produces less of thatsubstance.

Condition Effect

Figure 24Ammonium sulfate and ammo-nium phosphate are beingdropped from the airplane as fireretardants. The red dye used foridentification fades away after afew days.


ENVIRONMENTALSCIENCEAll living things neednitrogen, which cycles

through the environment. Nitro-gen gas, N2, is changed toammonia by bacteria in soils.Different bacteria in the soilchange the ammonia to nitritesand nitrates. Nitrogen in theform of nitrates is needed byplants to grow. Animals eatthe plants and deposit nitrogencompounds back in the soil.When plants or animals die,nitrogen compounds are alsoreturned to the soil. Additionalbacteria change the nitrogencompounds back to nitrogengas, and the cycle can startagain.


Le Châtelier’s principle can be used to control reactionsIf you raise the temperature, Le Châtelier’s principle indicatesthat the equilibrium will shift to the left, the direction thatabsorbs energy and makes less ammonia. If you raise the pres-sure, the equilibrium will move to reduce the pressure accordingto Le Châtelier’s principle. One way to reduce the pressure is tohave fewer gas molecules. This means the equilibrium moves tothe right—more ammonia—because there are fewer gas mol-ecules on the right side. So to get the most ammonia from thisreaction, you need to use a high pressure and a low temperature.The Haber process is a good example of balancing equilibriumconditions to make the most product. A manufacturing plant that uses the Haber process to produce ammonia is shown inFigure 25.

212 C H A P T E R 6


1. List five factors that may affect the rate of a chemical reaction.

2. Describe what can happen to the reaction rate of a systemthat is heated and then cooled.

3. Compare and Contrast a catalyst and an inhibitor.

4. Analyze the error in reasoning in the following situation: Aperson claims that because the overall amounts of reactantsand products don’t change, a reaction must have stopped.

5. Decide which way an increase in pressure will shift the fol-lowing equilibrium system involving ethane, C2H6, oxygen,O2, water, H2O, and carbon dioxide, CO2.

2C2H6 (gas) � 7O2 (gas) →← 6H2O (liquid) � 4CO2 (gas)

6. Identify and Explain an example of Le Châtelier’s principle.

7. Identify the effect of the following changes on the system inwhich the reversible reaction shown below is taking place:

4HCl (gas) � O2 (gas) →← 2Cl2 (gas) � 2H2O (gas) � heata. the pressure of the system is increasedb. the pressure of the system is decreasedc. the concentration of O2 is decreasedd. the temperature of the system is increased

8. Critical Thinking Consider the decomposition of solid calciumcarbonate to solid calcium oxide and carbon dioxide gas.

heat � CaCO3→← CaO + CO2 (gas)

What conditions of temperature and pressure would youchoose to get the most decomposition of CaCO3? Explain.

S U M M A R Y> Increasing the temperature,

surface area, concentration,or pressure of reactantsmay speed up chemicalreactions.

> Catalysts alter the rate ofchemical reactions. Mostcatalysts speed up chemicalreactions. Others, calledinhibitors, slow reactionsdown.

> In a chemical reaction,chemical equilibrium isachieved when reactantschange to products andproducts change to reac-tants at the same time andthe same rate.

> At chemical equilibrium, nochanges are apparent eventhough individual particlesare reacting.

> Le Châtelier’s principlestates that for any changemade to a system in equi-librium, the equilibrium willshift to minimize the effectsof the change.

Figure 25Ammonia, which is manufacturedin plants such as this, is used tomake ammonium perchlorate—one of the space shuttle’s fuels.


M A T H S K I L L S 213

Using Mole Ratios to Calculate MassDetermine the mass of hydrogen gas, H2, and oxygen gas, O2, produced by 4 mol ofwater, H2O, in the following chemical reaction:

2H2O → 2H2 � O2

Write down the mole ratio for the balanced equation and multiply theratio to obtain the number of moles of H2O.

There are 4 mol of H2O, so multiply each number in the ratio by 2.

Determine the mass per mol of each substance.

Look up the atomic mass of each element first. Since there are 2 hydrogenatoms and 1 oxygen atom in each molecule of H2O, the mass per mol of H2Ois 2 � 1 g/mol � 16 g/mol � 18 g/mol. Similarly, the mass of H2 is 2 g/mol,and the mass of O2 is 32 g/mol.

Multiply the number of moles by the mass per mol of each substance.

The total mass of the reactants should match the total mass of the products.

4 mol of H2O (72 g) will produce 8 g of H2 and 64 g of O2.

1. Determine the mass of H2SO4 produced when 1 mol of H2O reacts with 1 mol of SO3

in the following reaction:H2O � SO3 → H2SO4

2. Determine the mass of ZnSO4 produced in the following reaction if 2 mol of Zn reactswith 2 mol of CuSO4.

Zn � CuSO4 → ZnSO4 � Cu

3

2

1

Math SkillsMath SkillsMath Skills

Equation 2H2O → 2H2 � O2

Mole ratio 2 : 2 : 1

Amount (mol) 4 4 2

Equation 2H2O → 2H2 � O2

Mole ratio 2 : 2 : 1

Amount (mol) 4 4 2

Mass per mol 18 g/mol 2 g/mol 32 g/mol

Mass 18 g/mol � 4 mol � 2 g/mol � 4 mol � 32 g/mol � 2 mol

Total mass 72 g � 8 g � 64 g

PracticePractice


7. In any chemical equation, the arrow meansa. “equals.”b. “is greater than.”c. “yields.”

8. Hydrogen peroxide, H2O2, decomposes toproduce water and oxygen gas. The bal-anced equation for this reaction isa. H2O2 → H2O � O2.b. 2H2O2 → 2H2O � O2.c. 2H2O2 → H2O � 2O2.d. 2H2O2 → 2H2O � 2O2.

9. Which of the following chemical equationsis balanced?a. Fe � O2 → Fe2O3

b. Ca � SbCl3 → Si � Sb � 3CaCl2c. 3CuCl2 � 2Al → 2AlCl3 � 3Cud. CS2 � 2O2 → CO2 � SO2

10. Most reactions speed up whena. the temperature is lowered.b. equilibrium is achieved.c. the concentration of the products is

increased.d. the reactants are in small pieces.

11. Enzymesa. can be used to speed up almost any

chemical reaction.b. rely on increased surface area to catalyze

reactions.c. catalyze specific biological reactions.d. always work faster at higher temperatures.

12. A system in chemical equilibriuma. has particles that don’t move.b. responds to minimize change.c. is undergoing visible change.d. is stable only when all of the reactants

have been used.

Chapter HighlightsBefore you begin, review the summaries of thekey ideas of each section, found at the end ofeach section. The key vocabulary terms arelisted on the first page of each section.

1. When a chemical reaction occurs, atoms arenevera. ionized. c. destroyed.b. rearranged. d. vaporized.

2. In an exothermic reaction,a. energy is conserved.b. the formation of bonds in the product

releases more energy than is required tobreak the bonds in the reactants.

c. energy is released as bonds form.d. All of the above

3. Which of the following is an endothermicreaction?a. fireworks exploding in the skyb. water boilingc. photosynthesisd. respiration

4. A � B → AB is an example of aa. synthesis reaction.b. decomposition reaction.c. single-displacement reaction.d. double-displacement reaction.e. redox reaction.

5. Which of the following reactions is not anexample of a redox reaction?a. combustion c. dissolving in salt waterb. rusting d. cellular respiration

6. Radicalsa. form ionic bonds with other ions.b. result from broken covalent bonds.c. usually break apart to form smaller

components.d. bind molecules together.

UNDERSTANDING CONCEPTSUNDERSTANDING CONCEPTS

214 C H A P T E R 6

R E V I E WC H A P T E R 6


13. Explain what it means when a system inequilibrium shifts to favor the products.

14. When wood is burned, energy isreleased in the forms of heat andlight. Describe the reaction, andexplain why this change does notviolate the law of conservation of energy.Use the terms combustion, exothermic,and chemical energy.

15. Translate the following chemical equationinto a sentence.

CH4 � 2O2 → CO2 � 2H2O

16. Explain the difference between an exother-mic reaction and an endothermic reaction,and give an example of each.

17. How is a synthesis reaction different from adecomposition reaction?

18. How does a combustion reaction differ fromother chemical reactions?

19. Use the kinetic theory to explain how anincrease in the surface area of a reactantand higher temperatures can increase therate of a chemical reaction.

20. For each of the following changes to theequilibrium system below, predict whichreaction will be favored—forward (to theright), reverse (to the left), or neither.

H2 (gas) � Cl2 (gas) 2HCl (gas) � heat

a. addition of Cl2b. removal of HClc. increased pressured. decreased temperaturee. removal of H2

21. Graphing A technician carried out an experi-ment to study the effect of increasing temper-ature on a certain reaction. Her results areshown in the graph above.

a. Between which temperatures does therate of the reaction rise?

b. Between which temperatures does therate of the reaction slow down?

c. At what temperature is the rate of thereaction fastest?

22. Chemical Equations In 1774, JosephPriestly discovered oxygen when he heatedsolid mercury(II) oxide, HgO, and producedthe element mercury and oxygen gas. Writeand balance this equation.

23. Chemical Equations Write the balancedchemical equation for methane, CH4, react-ing with oxygen gas to produce water andcarbon dioxide.


USING VOC ABULARYUSING VOC ABULARY

BUILDING MATH SKILLSBUILDING MATH SKILLS

BUILDING GR APHING SKILLSBUILDING GR APHING SKILLS

6.0

5.0

4.0

3.0

2.0

1.0

020 40

Temperature (°C)

Rat

e of

rea

ctio

n (m

g pr

oduc

t pe

r m

inut

e)

10 30 50

WRITINGS K I L L

→ →


24. Chemical Equations Aluminum sulfate,Al2(SO4)3, is used to fireproof fabrics and tomake antiperspirants. It can be formed froma reaction between aluminum oxide, Al2O3,and H2SO4.

Al2O3 � 3H2SO4 → Al2(SO4)3 � 3H2O

a. How many moles of Al2(SO4)3 would beproduced if 6 mol of H2SO4 reacted withan unlimited amount of Al2O3?

b. How many moles of Al2O3 are required to make 9 mol of H2O?

c. If 588 mol of Al2O3 reacts with unlimitedH2SO4, how many moles of each of theproducts will be produced?

25. Chemical Equations Sucrose, C12H22O11, isa sugar used to sweeten many foods. Insidethe body, it is broken down to produce H2Oand CO2.

C12H22O11 � 12O2 → 12CO2 � 11H2O

List all of the mole ratios that can be deter-mined from this equation.

26. Chemical Equations Sulfur burns in air toform sulfur dioxide.

S � O2 → SO2

a. What mass of SO2 is formed from 64 gof sulfur?

b. What mass of sulfur is necessary toform 256 g of SO2?

27. Chemical Equations Zinc metal will reactwith hydrochloric acid, HCl, to producehydrogen gas and zinc chloride, ZnCl2.Write and balance the chemical equation for this reaction.

28. Chemical Formulas What is the mass of25 moles of water, H2O?

216 C H A P T E R 6

R E V I E WC H A P T E R 6

THINKING CR ITIC ALLYTHINKING CR ITIC ALLY

+

+

+ +

→

→

→

29. Designing Systems Paper consists mainlyof cellulose, a complex compound made upof simple sugars. Suggest a method for turn-ing old newspapers into sugars using anenzyme. What problems would there be?What precautions would need to be taken?

30. Applying Knowledge Molecular models ofsome chemical reactions are pictured below.Correct the drawings by adding coefficients or drawing moleculeswith a computer drawing programto reflect balanced equations.

a.

b.

c.

31. Creative Thinking Explain why hydrogengas is given off when a reactive metal under-goes a single-displacement reaction withwater.

32. Applying Knowledge Classify each of the fol-lowing reactions as synthesis, decomposition,single-displacement, double-displacement,or combustion:a. N2 � 3H2 → 2NH3

b. 2Li � 2H2O → 2LiOH � H2

c. 2NaNO3 → 2NaNO2 � O2

d. 2C6H14 � 19O2 → 12CO2 � 14H2Oe. NH4Cl → NH3 � HClf. BaO � H2O → Ba(OH)2

g. AgNO3 � NaCl → AgCl � NaNO3

COMPUTERS K I L L


33. Making Decisions Cigarette smoke containscarbon monoxide. Why do you think carbonmonoxide is in the smoke? Why is smokingbad for your health?

34. Interpreting and Communicating Chooseseveral items labeled “biodegradable,” andresearch the decomposition reactions involved.Write balanced chemical equations for thedecomposition reactions. Be sure to noteany conditions that must occur for the sub-stance to biodegrade. Present your informa-tion to the class to inform the studentsabout what products are best for the environment.

35. Integrating Biology Research the enzymeslisted in the table called “Common Enzymesand Their Uses” in Section 4. Write a para-graph on each one, describing in what wayit acts as a catalyst.

36. Integrating Physics Explain how a balancedchemical equation illustrates that mass isnever lost or gained in a chemical reaction.

37. Concept Mapping Copy the unfinished con-cept map given below onto a sheet of paper.Complete the map by writing the correctword or phrase in the lettered box.


DEVELOPING LI FE/WORK SKILLSDEVELOPING LI FE/WORK SKILLS

INTEGR ATING CONCEPTSINTEGR ATING CONCEPTS

breaking

c.

a.

Heat

f.

d.

formation

g.

reactions

b.

is released in

that involve

is absorbed in

in which one in which two

e. h.

exchange to form a

i. j. k.

and

replaces another,depending on

such as a

Art Credits: Fig. 2, Kristy Sprott; Fig. 4, Kristy Sprott; “Real World Applications”, Uhl Studios, Inc.;Fig. 5-6, Kristy Sprott; Fig. 8-9, Kristy Sprott; p. 156, Kristy Sprott; Fig. 10-11, Kristy Sprott; Fig. 13,Kristy Sprott; p. 164, Kristy Sprott; Fig. 16, Kristy Sprott; Fig. 18, Kristy Sprott; Fig. 22, Kristy Sprott;“Thinking Critically”, Kristy Sprott.

Photo Credits: Chapter opener image of grilled vegetables by Rita Moss/Getty Images/The ImageBank; burning charcoals by Charles O’ Rear/CORBIS; Fig. 1A, 1B Charlie Winters/HRW; Fig. 1C,Charlie Winters; Fig. 2, Peter Van Steen/HRW; Fig. 3, E. R. Degginger/Color-Pic, Inc.; Fig. 6, Peter Van Steen/HRW; Fig. 7A, E. R. Degginger/Color-Pic, Inc.; Fig. 7B, Runk/Schoenberger/Grant HeilmanPhotography; Fig. 8, Sergio Purtell/Foca/HRW; “Science and the Consumer,” Peter Van Steen/HRW;FIg. 10, 11, Sergio Purtell/Foca/HRW; “Connection to Fine Arts,” Andy Levin/Photo Researchers, Inc.;Fig. 12, Charlie Winters; Fig. 13, Hank Morgan/Photo Researchers, Inc.; Fig. 14, Sam Dudgeon/HRW;Fig. 15, Visuals Unlimited/John Sohldon; Fig. 17, Charlie Winters; Fig. 18, NASA; FIg. 19, SergioPurtell/Foca/HRW; Fig. 20, Peter Van Steen/HRW; Fig. 21, Dr. Thomas A. Steitz/Yale University, Fig. 22, Sam Dudgeon/HRW; Fig. 23, SuperStock; Fig. 24, Visuals Unlimited/Steve McCutcheon; Fig. 25, Visuals Unlimited/Tom J. Ulrich; “Skills Practice Lab,” Sam Dudgeon/HRW.

www.scilinks.orgTopic: Biodegradable SciLinks code: HK4015


Measuring the Rate of aChemical Reaction

� Procedure

Observing the Reaction BetweenZinc and Hydrochloric Acid

1. On a blank sheet of paper, prepare a table like theone shown at right.SAFETY CAUTION Hydrochloric acid can cause severeburns. Wear a lab apron, gloves, and safety goggles. If you get acid on your skin or clothing, wash it off at the sink while calling to your teacher. If you getacid in your eyes, immediately flush it out at the eyewash station while calling to your teacher.Continue rinsing for at least 15 minutes or until help arrives.

2. Fill a 10 mL graduated cylinder with water. Turn thecylinder upside down in a beaker of water, taking careto keep the cylinder full. Place one end of the rubbertubing under the spout of the graduated cylinder.Attach the other end of the tubing to the arm of theflask. Place the flask in a water bath at room tempera-ture. Record the initial gas volume of the cylinder andthe temperature of the water bath in your data table.

3. Cut a piece of zinc about 50–75 mm long. Measurethe length, and record this in your data table. Placethe zinc in the sidearm flask.

4. Measure 25 mL of hydrochloric acid in a graduatedcylinder.

5. Carefully pour the acid from the graduated cylinderinto the flask. Start the stopwatch as you begin to pour.Stopper the flask as soon as the acid is transferred.

6. Record any signs of a chemical reaction you observe.

7. After 15 minutes, determine the amount of gas givenoff by the reaction. Record the volume of gas in yourdata table.

How can you show that the rate of achemical reaction depends on the tem-perature of the reactants?

> Measure the volume of gas evolvedto determine the average rate of thereaction between zinc and hydro-chloric acid.

> Determinehow the rate of this reactiondepends on the temperature of thereactants.

beaker to hold a 10 mL graduatedcylinder

graduated cylinder, 10 mLgraduated cylinder, 25 mLheavy scissorshydrochloric acid, 1.0 Micemetric rulerrubber tubingsidearm flasks with rubber stoppers (2)stopwatchstrips of thick zinc foil, 10 mm widethermometerwater bath to hold a sidearm flask

USING SCIENTIFIC METHODS

Introduction

Objectives

Materials

218 C H A P T E R 6 Copyright © by Holt, Rinehart and Winston. All rights reserved.

Designing Your Experiment8. With your lab partners decide how you will answer the question posed at the

beginning of the lab. By completing steps 1–7, you have half the data you needto answer the question. How can you collect the rest of the data?

9. In your lab report, list each step you will perform in your experiment. Becausetemperature is the variable you want to test, the other variables in your experi-ment should be the same as they were in steps 1–7.

10. Before you carry out your experiment, your teacher must approve your plan.

Performing Your Experiment11. After your teacher approves your plan, carry out your experiment. Record your

results in your data table.

12. How do the two reactions differ?

� Analysis1. Express the rate of each reaction as mL of gas

evolved in 1 minute.

2. Which reaction was more rapid?

3. Divide the faster rate by the slower rate, andexpress the reaction rates as a ratio.

4. According to your results, how does decreasingthe temperature affect the rate of a chemicalreaction?

� Conclusions5. How could you test the effect of temperature

on this reaction without using an ice bath?

6. How can you express the rate of each of thetwo reactions you conducted as a function ofthe surface area of the zinc?

7. How would you design an experiment to testthe effect of surface area on this reaction?

Length of Initial gas Final gaszinc strip volume volume Temperature Reaction

(mm) (mL) (mL) (ºC) time (s)

Reaction 1

Reaction 2


viewpoints

How Should Life-Saving Inventions Be Introduced?

viewpointsviewpoints

220 V I E W P O I N T S

Researchers are developing better fireproofmaterials to use inside passenger air-planes. But the new materials are much

more expensive than the ones currently used.Should the Federal Aviation Administration

(FAA) require that the new materials be usedon all new and old planes, or should it be upto the plane manufacturers and airlines todecide whether to use the new materials?

A similar debate occurs whenever life-savinginventions are introduced, from automobile

airbags to better child-safety seats. If theinventions should be used, who should bearthe cost? Should it be the federal government,an insurance company, a manufacturer, or thecustomers?

If the device shouldn’t be required at alltimes, how do you decide when it should beused? When are the risks so small that it doesn’t make sense to spend money on another safety device?

What do you think?

> FROM: Stacey F., Rochester, MN.

It should be up to the plane manufactuersbecause not all companies would be able toafford the cost. The FAA should look intothe budgets of all plane companies and companies that can afford it should

be required to use

the new material.

Leave the Decisionsto the Companies Involved

Leave the Decisions to the Companies Involved

> FROM: Virginia M., Houston, TX

The airlines are responsible for the lives of their passen-gers, so they should decide. But the FAA should pass a law stating that if the airlines refuse new safety meas-ures, the airlines will accept total responsibility for anyaccidents that occur.

> FROM: Emily B., Coral Springs, FL

I think it should be up to the plane manu-facturers and airlines. The new materialsshouldn’t be required on planes that arealready built or on planes that are beingbuilt, because of expenses. However, itwould be to an airline’s advantage to havethe best safety material possible for theircustomers’ sake.


Your Turn Your Turn >>

Require Safety ImmediatelyRequire SafetyImmediately

> FROM: April R., Coral Springs, FL

If it can save just one life, it’s worth spending money andtime on. Eventually the technology will be required on allplanes anyway. If an airline chose not to use these materi-als and there were an accident, there would be liabilitycases because lives might have been saved. Most people will have no problem spending more for a plane ticket if their safety is ensured.

> FROM: Carlene de C., Chicago, IL

The FAA should require that all planes—

those currently in use and those being

built—have fireproof materials. Other-

wise, passengers could sue the airline

company if they were hurt in a fire and

it could have been prevented.

1. Critiquing Viewpoints Select one ofthe statements on this page that youagree with. Explain at least one weakpoint in the statement. How would yourespond to someone who used thispoint as a reason you were wrong?

2. Critiquing Viewpoints Select one ofthe statements on this page that youdisagree with. Explain one strongpoint in the statement. How wouldyou respond to someone who usedthis point as a reason they were right?

3. Life/Work Skills Imagine that you arepreparing to testify in a congressionalhearing about this matter. Choose thefour most important points you’dmake, and draft a statement thatexplains all of them persuasively.

4. Working Cooperatively With yourteacher’s help, stage a role-playingexercise, with students serving as thepanel of congressional representativespreparing to vote on this issue and aswitnesses for the airlines, the airplanemanufacturers, insurance companies,safety organizations, and a passenger’srights group.

> FROM: Shannon B., Bowling Green, KY.

They should put the new fireproof materials on all planes, even the ones that have alreadybeen built. The public’s health is at risk if a plane malfunctions, and the airlines should want to keep everybody safe. Otherwise they will lose customers.

TOPIC: LifesavingTechnology

GO TO: go.hrw.comKEYWORD: HK4 Lifesavers

What do you think should be done? Why? Share your views on this issue and learn about other viewpoints at the HRW Web site.

221Copyright © by Holt, Rinehart and Winston. All rights reserved.

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CHAPTER 6 Chemical Reactions - Grygla Public School 6 Chemical Reactions ... sugar to form new substances, ... of metal alloy and begins to cor-rode the metals vigorously. Then