Chemical Reactions

Dehydration of Sugar

Sugar and Sulfuric Acid yield Carbon and Water

C12H22O11 + H2SO4 → 12 C + 11 H2O

Conservation of Mass

• C12H22O11 + H2SO4 → 12 C + 11 H2O

• Is this equation balanced?

C H O S C H O S

The number of atoms of each element on the left much be equal to the number of each on the right.

Conservation of Mass• C12H22O11 + H2SO4 → 12 C + 11 H2O

• Is this equation balanced?

C H O S C H O S

12 24 15 1 12 22 11 0

The number of atoms of each element on the left much be equal to the number of each on the right.

• It is not balanced. In actuality, the situation is a little more complicated than this.

Conservation of Mass

C12H22O11(s) + H2SO4(aq) + 1/2 O2(g) → 11C(s) + CO2(g) + 12H2O(g) + SO2(g)

Is this chemical equation balanced?

C H O S C H O S

The number of atoms of each element on the left much be equal to the number of each on the right.

Conservation of Mass

C12H22O11(s) + H2SO4(aq) + 1/2 O2(g) → 11C(s) + CO2(g) + 12H2O(g) + SO2(g)

Yes it is!

C H O S C H O S

12 24 16 1 12 22 16 1

The number of atoms of each element on the left much be equal to the number of each on the right.

1. Combination Reaction2. Decomposition Reaction3. Single Replacement Reactions4. Double Replacement Reactions5. Combustion Reactions

Five Types of Chemical Reactions

Combination Reaction• A combination or synthesis reaction is a chemical

change in which two or more substances react to form a single new substance.

• General Equation:• X + Y XY

• Example• Magnesium combines with Oxygen to

form magnesium oxide. Formula?

Combination Reaction• A combination or synthesis reaction is a chemical

change in which two or more substances react to form a single new substance.

• General Equation:• X + Y XY

• Example• Magnesium combines with Oxygen to

form magnesium oxide. Formula?• Mg + O2 MgO balanced?

Combination Reaction• A combination or synthesis reaction is a chemical

change in which two or more substances react to form a single new substance.

• General Equation:• X + Y XY

• Example• Magnesium combines with Oxygen to form

magnesium oxide. Formula?• Mg + O2 MgO balanced?

• 2Mg + O2 2MgO

Combination Reaction

• Examples• 2K(s) +Cl2(g) 2KCl(s)

• S + O2 SO2

• Fe(s) + S(s) FeS(s)• Fe(s) + 3S(s) Fe2S3 (s)

Name these products!

Combination Reaction

• Examples• 2K(s) +Cl2(g) 2KCl(s)

• S + O2 SO2

• Fe(s) + S(s) FeS(s)• Fe(s) + 3S(s) Fe2S3 (s)

Name these products!

• Potassium Chloride• Sulfur Dioxide• Iron (II) Sulfide• Iron (III) Sulfide

Copper and Sulfur• Cu(s) + S(s) ??? (two reactions possible)

• Finish this equation.

Copper and Sulfur• Cu(s) + S(s) CuS(s)• Is this balanced?• Copper is a transition metal• Cu+ and Cu+2

For Copper (II)• Cu(s) + S(s) CuS(s) (balanced)For Copper (I)• Cu(s) + S(s) Cu2S(s) (not balanced)• 2Cu(s) + S(s) Cu2S(s) (balanced)

Assignment #1

• Complete and balance this equation for this combination reaction:

Be + O2

• Write and balance the equation for the formation of magnesium nitride.

Two Questions:

• Complete and balanced this equation for a combination reaction:

Be + O2

2Be + O2 2BeO

• Write and balance the equation for the formation of magnesium nitride from is elements.

3Mg + N2 Mg3N2

Decomposition Reaction

• A decomposition reaction is a chemical change in which a single compound breaks down into two or more substances.

• General Equation: X Y X +Y

• Mercury (II) Oxide decomposes into Mercury and Oxygen.

Decomposition Reaction

• A decomposition reaction is a chemical change in which a single compound breaks down into two or more substances.

• General Equation: X Y X +Y

• Mercury (II) Oxide decomposes into Mercury and Oxygen.

• 2HgO(s) 2Hg(l) + O2(g)•

Trinitrotoluene• Some of the explosive

properties of dynamite are attributed to a decomposition reaction which produces large amounts of gas!

• For every 2 moles of TNT that decomposes, 15 moles of hot, expanding gases are produced.

• C7H5N3O6 -- TNT

C7H5N3O6 (s) N2(g) + CO(g) + H2O(g) + C(s). Balance me!

Trinitrotoluene• Some of the explosive

properties of dynamite are attributed to a decomposition reaction which produces large amounts of gas!

• For every 2 moles of TNT that decomposes, 15 moles of hot, expanding gases are produced.

• C7H5N3O6 -- TNT

2C7H5N3O6 (s) 3N2(g) + 7CO(g) + 5H2O(g) + 7C(s).

Decomposition Reactions do not have to break down into elements.

• 2H2O2 2H2O + O2

• H2CO3 H2O + CO2

• What type of Acid is this?• What are the Products?

ELEPHANT TOOTHPASTE 50ml 30% H2O2 + 10ml Sat. KI + Soap & Food Coloring

Decomposition of Hydrogen Peroxide:

• H2O2(aq) → 2 H2O(l) + O2(g)

• Use KI as a Catalyst!• H2O2(aq) + I-(aq) → OI-(aq) + H2O(l)

• H2O2(aq) + OI-(aq) → I-(aq) + H2O(l) + O2(g)

• KI-(aq) disassociates and the Iodide ion decomposes a hydrogen peroxide molecule resulting in the formation of an OI- ion which decomposes another hydrogen peroxide molecule producing a new Iodide ion which can decompose another hydrogen peroxide molecule and so on…..

• A CATALYST speeds up a chemical reaction!

ASSIGNMENT

• Complete and Balance this Decomposition Reaction: HI

• Through electrolysis, Water Breaks down into Hydrogen and Oxygen. Balanced Chemical Equation?

• Write the formula for the binary compound that decomposes to the products H2 and Br2

ASSIGNMENT

• Complete and Balance this Decomposition Reaction: HI

• Through electrolysis, Water Breaks down into Hydrogen and Oxygen. Balanced Chemical Equation?

• Write the formula for the binary compound that decomposes to the products H2 and Br2

2HI H2 and I2

2H2O 2H2 + O2

2HBr H2 + Br2

Decomposition: Genie in a bottle

2H2O2 --> O2 + 2H2O

This reaction is usually very slow but can be increased via a catalyst.

MnO2 + 2H2O2 --> Mn + O2 + 2H2O

Single Replacement Reaction

• A single replacement reaction is a chemical change in which one element replaces a second element in a compound.

• General Equation:• W + X Y WY + X

• Examples• Zn(s) + Cu(NO3)2(aq) Cu(s) +Zn(NO3)2(aq)

• Br2(aq) + NaI(aq) ?

• Mg(s) + HCl(aq) ?

Single Replacement Reaction• A single replacement reaction is a chemical change in which

one element replaces a second element in a compound. A halogen can replace a less reactive halogen. A reactive metal will replace any less reactive metal.

• General Equation:• W + X Y WY + X

• Examples• Zn(s) + Cu(NO3)2(aq) Cu(s) + Zn(NO3)2(aq)

• Br2(aq) + 2NaI(aq) 2NaBr(aq) +I2(aq)

• Mg(s) + 2HCl(aq) MgCl2 + H2(g)

Notice how a cation replaces a cation and an anion replaces an anion.

Assignment:

• Zn(s) +H2SO4(aq)

• Cl2(aq)+ NaBr(aq)

• Fe(s) + Pb(NO3)2(aq)

• Al(s) + CuCl2(aq)

• Cl2(aq) + NaI(aq)

• Ca(s) + H2O(l)

Assignment• Zn(s) +H2SO4(aq)

• Cl2(aq)+ NaBr(aq)

• Fe(s) + Pb(NO3)2(aq)

• Al(s) + CuCl2(aq)

• Cl2(aq) + NaI(aq)

• Ca(s) + H2O(l)

• Zn(s) +H2SO4(aq) ZnSO4(aq) + H2(g)

• Cl2(aq) +NaBr(aq) NaCl (aq) + Br2(aq)

• Cl2(aq) + 2NaBr(aq) 2NaCl(aq) + Br2(aq)

• Fe(s) + Pb(NO3)2(aq) Fe(NO3)2(aq) +Pb(s)

• Al(s) + CuCl2(aq) Cu(s) + AlCl3(aq)

• 2Al(s) + 3CuCl2(aq) 3Cu(s) + 2AlCl3(aq)

• Cl2(aq) + NaI(aq) l2(aq) + NaCl(aq)

• Cl2(aq) + 2NaI(aq) l2(aq) + 2NaCl(aq)

• Ca(s) + 2H2O(l) + Ca(OH)2(aq) H2(g)

Double Replacement Reaction

• A double replacement reaction is a chemical change involving an exchange of positive ions (cations) between two compounds. Often involve the formation of a precipitate, a gaseous product or water.

• General Equation:

• A+B- +C+D- A+D- + B+C-

• Examples• Na2S(aq) + Cd(NO3)2(aq) CdS(s) + 2NaNO3(aq) (precipitate forms)

• 2NaCN (aq) + H2SO4(aq) 2HCN(g) +Na2SO4(aq) (poisonous gas)

• Ca(OH)2(aq) + 2HCl(aq) CaCl2(aq) + 2H2O)(l) (water forms)

Activity Series

Double Replacement Reaction

• A double replacement reaction is a chemical change involving an exchange of positive ions (cations) between two compounds. Often involve the formation of a precipitate, a gaseous product or water.

• General Equation:

• A+B- +C+D- A+D- + B+C-

• Examples• Na2S(aq) + Cd(NO3)2(aq) CdS(s) + 2NaNO3(aq) (precipitate forms)

• 2NaCN (aq) + H2SO4(aq) 2HCN(g) +Na2SO4(aq) (poisonous gas)

• Ca(OH)2(aq) + 2HCl(aq) CaCl2(aq) + 2H2O)(l) (water forms)

Combustion Reaction• A combustion reaction is a chemical change in which an element or

compound reacts with oxygen often producing energy in the form of heat and light . Oxygen is always a reactant and usually there is a hydrocarbon as a reactant.

• General Equation:

• X + O2 Y

• Examples• Burning of a magnesium strip is a simple combination reaction but it is also classifiable as a

combustion reaction.

• 2Mg(s) + 02(g) 2MgO(s)

• Similarly S(s) +O2(g) SO2(g)

Combustion Of Hydro-CarbonsYield CO2 and H2O

Combustion of Methane (CH4) which is natural gas or what powers our Bunsen burners.

CH4 + 202 CO2 + 2H2O

Combustion of Gasoline (2C8H18) which is a mixture of many different and around 100 different liquids.

2C8H18(l) + 25 O2 (g) →16 CO2(g)+ 18H2O(l)

Combustion of Isopropyl Alcohol (C3H8O) which is not a hydrocarbon but has the same products as hydrocarbons.

2C3H8O(l) + 9O2(g) ----> 6CO2 (g) + 8H2O(g)

Nitrogen and Sulfur If you were to add in Nitrogen or Sulfur then you would just include NO2 or SO2 as products as well.

Combustion Of Hydro-CarbonsYield CO2 and H2O

Combustion of Methane (CH4) which is natural gas or what powers our Bunsen burners.

CH4 + 202 CO2 + 2H2O

Combustion of Gasoline (2C8H18) which is a mixture of many different and around 100 different liquids.

2C8H18(l) + 25 O2 (g) →16 CO2(g)+ 18H2O(l)

Combustion of Isopropyl Alcohol (C3H8O) which is not a hydrocarbon but has the same products as hydrocarbons.

2C3H8O(l) + 9O2(g) ----> 6CO2 (g) + 8H2O(g)

Nitrogen and Sulfur If you were to add in Nitrogen or Sulfur then you would just include NO2 or SO2 as products as well.

Could you drive a car on the moon?

Assignment: Combustion Problems

• Benzene C6H6

• Ethanol CH3CH2OH• Formic Acid HCOOH• Heptane C7H16

• Glucose C6H12O6

• Sucrose C12H22O11

Fuego!!!Read the article on Page 340-341 of your text book. Answer these questions.

• What three things are needed for fire to burn?

• Why is it unsafe to use a single kind of fire extinguisher?

• Why do you want to stop, drop and roll when on fire?

• What do the letters A,B,C, and D refer to when dealing with fires.

• Task: Contact your local fire department and obtain statistics on how many class A,B,C,D fires have occurred in their area in the past 6 months or year.

• As a class we will create a bar graph of the results.

Fuego!!!• What three things are needed

for fire to burn?

• Why is it unsafe to use a single kind of fire extinguisher?

• Why do you want to stop, drop and roll when on fire?

• What do the letters A,B,C, and D refer to when dealing with fires.

1. Fuel, Oxygen and Energy2. A fire extinguisher that controls one type of fire

may enhance other types of combustion reactions. Spraying water on a magnesium fire will decompose the water into flammable hydrogen and oxygen gas. Also, water will spread a grease fire.

3. You can smother the fire by removing the air around it and the ground is cooler so it can absorb some heat lowering the temperature. Put noncombustible dirt on your clothes.

4. A ordinary combustibles, plastic wood, B involve flammable liquids such as gasoline, C fires are electrical, D are metal fires.

Model a Fire Extinguisher• Background: CO2 fire extinguishers are

used to put out grease fires. Why would you not want to use water based fire extinguishers?

• Purpose: observe the effect of carbon dioxide on a flame.

• Materials: Calcium Carbonate, dilute hydrochloric acid, 3 beakers, candle, matches.

• Procedure: place a small amount of calcium carbonate in a beaker. Add hydrochloric acid and allow several minutes for the reaction to produce collectible carbon dioxide gas. Collect the gas in a second beaker and pour it into a third beaker with a lit candle in it.

1. What happened to the lit candle?

2. Which is heavier, air or CO2? Don’t guess, determine the molecular weight of each.

3. What is the difference between being combustible and flammable?

4. Is paper combustible or flammable?

5. Why does the collected CO2 stay in the beaker until you pour it on the flame.

Predicting the Formation of a Precipitate

11.3

You can predict the formation of a precipitate by using the general rules for solubility of ionic compounds.

Predicting the Formation of a Precipitate

11.3

Will a precipitate form when a sodium carbonate solution is mixed with a barium nitrate solution?

Predicting the Formation of a Precipitate

11.3

Will a precipitate form when a sodium carbonate solution is mixed with a barium nitrate solution?

Sodium nitrate is soluble but barium carbonate is insoluble. The net ionic equation is

Lab: Combustion of Steel/Magnesium• Purpose: Does steel get lighter

or heavier during after a combustion reaction?

• Materials: Superfine steel wool, plastic sandwich bag, ring stand, utility clamp, matches

• Safety: burns readily, goggles, standard safety procedures.

• Procedure: Determine mass of steel wool and a container. Burn the steel wool in a way that you can preserve the contents. Determine its mass.

• Prelab Question: What effect will burning the steel wool have on it?

• Postlab question: What effect did burning have on the steel wool.

• What type of reaction occurred? Write a balanced equation for it.

Combustion Part Duex

CxHy + (x +y/4)02 xCO2 + (y/2)H2OCombustion of Methane (CH4)

CxHy + (x +y/4)02 xCO2 + (y/2)H2OCH4 + (1+4/4)02 1CO2 + (4/2)H2OCH4 + 202 CO2 + 2H2O

Combustion of Gasoline which is a mixture of many different hydrocarbons but can be approximated as 2C8H18.CxHy + (x +y/4)02 xCO2 + (y/2)H2O

2C8H18(l) + 25 O2 (g) →16 CO2(g)+ 18H2O(l)

This is the reason your car works.