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Chemical Reactions

Section 9.1Reactions and Equations

Section 9.2 Classifying Chemical Reactions

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Section 9-1

Section 9.1 Reactions and Equations

Recognize evidence of chemical change.

Represent chemical reactions with equations.

Balance chemical equations.

Section 9-1

Section 9.1 Reactions and Equations

chemical change: a process involving one or more substances changing into a new substance

chemical reaction

reactant

product

chemical equation

coefficient

Section 9-1

Chemical Reactions

Chemical reaction:

The process by which one or more substances are rearranged to form different substances.

Section 9-1

Chemical Reactions (cont.)

Evidence of a chemical reaction

–Change in temperature

–Change in color

–Odor, gas, or bubbles

Section 9-1

Representing Chemical Reactions (cont.)

A chemical equation is a statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction.

Section 9-1

Representing Chemical Reactions

Two parts of chemical equations

Reactants are the starting substances.

Products are the substances formed in the reaction.

Section 9-1

Section 9-1

Representing Chemical Reactions (cont.)

aluminum(s) + bromine(l) → aluminum bromide(s)

Chemical Reaction in words

What state are the reactants?

What state is the product?

Section 9-1

Representing Chemical Reactions (cont.)

Skeleton equations use atomic symbols

Al(s) + Br(l) → AlBr3(s)

Notice the product is a correct molecular formula

Solid lithium reacts with chlorine gas to produce solid lithium chloride.

Example 1

Solid lithium reacts with chlorine gas to produce solid lithium chloride.

lithium(s) + chlorine(g) lithium chloride(s)

Example 1 word equation

Solid lithium reacts with chlorine gas to produce solid lithium chloride.

lithium(s) + chlorine(g) lithium chloride(s)

Li(s) + Cl2(g) LiCl(s)

Remember a lot of atoms are diatomic in nature

Example 1 skeleton equation

Nitrogen gas reacts with oxygen gas to produce nitrogen dioxide gas.

Example 2

Nitrogen gas reacts with oxygen gas to produce nitrogen dioxide gas.

nitrogen(g) + oxygen(g) nitrogen dioxide(g)

Example 2 word equation

Nitrogen gas reacts with oxygen gas to produce nitrogen dioxide gas.

nitrogen(g) + oxygen(g) nitrogen dioxide(g)

N2(g) + O2(g) NO2(g)

Example 2 skeleton equation

Solid iron reacts with aqueous copper (II) nitrate to produce solid copper and aqueous iron (II) nitrate.

Example 3

Solid iron reacts with aqueous copper (II) nitrate to produce solid copper and aqueous iron (II) nitrate.

Iron(s) + copper(II) nitrate(aq) copper(s) + iron(II) nitrate(aq)

Remember nitrate is (NO3) -

Example 3 word equation

Solid iron reacts with aqueous copper (II) nitrate to produce solid copper and aqueous iron (II) nitrate.

Iron(s) + copper(II) nitrate(aq) copper(s) + iron(II) nitrate(aq)

Fe(s) + Cu(NO3)2(aq) Cu(s) + Fe(NO3)2(aq)

Example 3 skeleton equation

Section 9-1

Balancing Chemical Equations

Balanced equation for the reaction between aluminum and bromine.

Section 9-1

Balancing Chemical Equations (cont.)

A coefficient in a chemical equation is the number written in front of a reactant or product.

It describes the lowest whole-number ratio. Yeah!!!!

Section 9-1

Balancing Chemical Equations (cont.)

Balanced equations represent the Law of Conservation of Mass

Section 9-1

Balancing Chemical Equations (cont.)

Li(s) + Cl2(g) LiCl(s)

1 Li 2 Cl 1 Li 1 Cl

Example 1 balanced equation

Li(s) + Cl2(g) LiCl(s)

1 Li 2 Cl 1 Li 1 Cl

need 2 Cl on this side

Example 1 balanced equation

Li(s) + Cl2(g) LiCl(s)

1 Li 2 Cl 1 Li 1 Cl

need 2 Cl on this side

put 2 in front of LiCl

Li(s) + Cl2(g) 2LiCl(s)

1 Li 2 Cl 2 Li 2 Cl

Example 1 balanced equation

Li(s) + Cl2(g) LiCl(s)

1 Li 2 Cl 1 Li 1 Cl

need 2 Cl on this side

Li(s) + Cl2(g) 2LiCl(s)

1 Li 2 Cl 2 Li 2 Cl bc molecule

need 2 Li

on this side put 2 in front of Li only

Example 1 balanced equation

Li(s) + Cl2(g) LiCl(s)1 Li 2 Cl 1 Li 1 Cl

need 2 Cl on this side

Li(s) + Cl2(g) 2LiCl(s)1 Li 2 Cl 2 Li 2 Cl bc moleculeNeed 2 Li

2Li(s) + Cl2(g) 2LiCl(s)2 Li 2 Cl 2 Li 2 Cl all balanced

Example 1 balanced equation

N2(g) + O2(g) NO2(g)

Example 2 balanced equation

N2(g) + O2(g) NO2(g) 2N 2O 1N 2O not balanced

put 2 in front of NO2

N2(g) + O2(g) 2NO2(g) 2N 2O 2N 4O not balanced

put 2 in front of O2

N2(g) + 2O2(g) 2NO2(g) 2N 4O 2N 4O balanced

Example 2 balanced equation

Fe(s) + Cu(NO3)2(aq) Cu(s) + Fe(NO3)2(aq)

Example 3 balanced equation

Fe(s) + Cu(NO3)2(aq) Cu(s) + Fe(NO3)2(aq)

1Fe 1Cu 2(NO3) 1Cu 1Fe 2(NO3)

balanced

Example 3 balanced equation

Solid potassium reacts with liquid water to produce hydrogen gas and a water (aqueous) solution of potassium hydroxide.

Hydroxide is OH-

Practice 1 balanced equation

Solid potassium reacts with liquid water to produce hydrogen gas and a water (aqueous) solution of potassium hydroxide.

Potassium(s) + water(l) hydrogen(g) + potassium

hydroxide(aq)

K(s) + H2O(l) H2(g) + KOH(aq)

Practice 1 balanced equation

Solid potassium reacts with liquid water to produce hydrogen gas and a water (aqueous) solution of potassium hydroxide.Potassium(s) + water(l) hydrogen(g) +

potassium hydroxide(aq)

K(s) + H2O(l) H2(g) + KOH(aq)

2K(s) + 2H2O(l) H2(g) + 2KOH(aq)

Practice 1 balanced equation

Calcium chloride and sodium carbonate in water (aqueous) solution produce solid calcium carbonate and a water solution of sodium chloride.

Carbonate is (CO3)-2

Practice 2 balanced equation

Calcium chloride and sodium carbonate in water (aqueous) solution produce solid calcium carbonate and a water solution of sodium chloride.

Calcium chloride(aq) + sodium carbonate(aq) calcium carbonate(s) + sodium chloride(aq)

CaCl2(aq) + Na2(CO3)(aq) Ca(CO3)(s) + NaCl(aq)

Practice 2 balanced equation

Calcium chloride and sodium carbonate in water (aqueous) solution produce solid calcium carbonate and a water solution of sodium chloride.

Calcium chloride(aq) + sodium carbonate(aq) calcium carbonate(s) + sodium chloride(aq)

CaCl2(aq) + Na2(CO3)(aq) Ca(CO3)(s) + NaCl(aq)

CaCl2(aq) + Na2(CO3)(aq) Ca(CO3)(s) + 2NaCl(aq)

Practice 2 balanced equation

Liquid bromine and solid lithium iodide react to form solid lithium bromide and solid iodine.

Practice 3 balanced equation

Liquid bromine and solid lithium iodide react to form solid lithium bromide and solid iodine.

bromine(l) + lithium iodide(s) lithium bromide(s) + iodine(s)

Br2(l) + LiI(s) LiBr(s) + I2(s)

Practice 3 balanced equation

Liquid bromine and solid lithium iodide react to form solid lithium bromide and solid iodine.

bromine(l) + lithium iodide(s) lithium bromide(s) + iodine(s)

Br2(l) + LiI(s) LiBr(s) + I2(s)

Br2(l) + 2LiI(s) 2LiBr(s) + I2(s)

Practice 3 balanced equation

A. A

B. B

C. C

D. D

Section 9-1

Section 9.1 Assessment

Which of the following is NOT a chemical reaction?

A.a piece of wood burning

B.a car rusting

C.an ice cube melting into water

D. red litmus paper turning blue

A. A

B. B

C. C

D. D

Section 9-1

Section 9.1 Assessment

What is the coefficient of bromine in the equation

2Al(s) + 3Br2(l) → 2AlBr3(s)?

A. 1

B. 2

C. 3

D. 6

End of Section 9-1

Section 9-2

Section 9.2 Classifying Chemical Reactions

Classify chemical reactions.

Identify the characteristics of different classes of chemical reactions.

Section 9-2

Section 9.2 Classifying Chemical Reactions (cont.)

Types of chemical reactions:• Synthesis• Combustion• Decomposition• Replacement reactions

Section 9-2

Section 9.2 Classifying Chemical Reactions

metal: an element that is a solid at room temperature, a good conductor of heat and electricity, and is generally shiny

synthesis reaction

combustion reaction

decomposition reaction

single-replacement reaction

double-replacement reaction

precipitate

Section 9-2

Types of Chemical Reactions

Synthesis reaction

two or more substances

react

produce a single product.

Section 9-2

Types of Chemical Reactions (cont.)

Synthesis Example

Section 9-2

Types of Chemical Reactions (cont.)

Combustion Reaction

oxygen combines with a substance

release energy in the form of heat and light

Section 9-2

Types of Chemical Reactions (cont.)

This is also a synthesis reaction.

Combustion Example

Section 9-2

Decomposition Reactions

Decomposition Reaction

a single compound breaks down into two or more elements or new compounds

Often require an energy source, such as heat, light, or electricity.

Section 9-2

Replacement Reactions

Single Replacement Reaction.

the atoms of one element replace the atoms of another element in a compound

A + BX → AX + B

Section 9-2

Replacement Reactions (cont.)

• A metal will not always replace a metal in a compound dissolved in water because of differing reactivities.

• An activity series can be used to predict if reactions will occur.

Section 9-2

Replacement Reactions (cont.)

• Halogens frequently replace other halogens in replacement reactions.

• Halogens also have different reactivities and do not always replace each other.

Section 9-2

Replacement Reactions (cont.)

Double replacement reactions

An ion exchange between two compounds

Section 9-2

Replacement Reactions (cont.)

Precipitate

the solid product produced during a chemical reaction

All double replacement reactions produce either water, a gas, or a precipitate.

Section 9-2

Replacement Reactions (cont.)

Section 9-2

Replacement Reactions (cont.)

A. A

B. B

C. C

D. D

Section 9-2

Section 9.2 Assessment

Which of the following is NOT one of the four types of reactions?

A.deconstructive

B.synthesis

C.single replacement

D.double replacement

A. A

B. B

C. C

D. D

Section 9-2

Section 9.2 Assessment

The following equation is what type of reaction?

KCN(aq) + HBr(aq) → KBr(aq) + HCN(g)

A.deconstructive

B.synthesis

C.single replacement

D.double replacement

End of Section 9-2

Section 9-3

Section 9.3 Reactions in Aqueous Solutions

Describe aqueous solutions.

Write complete ionic and net ionic equations for chemical reactions in aqueous solutions.

Predict whether reactions in aqueous solutions will produce a precipitate, water, or a gas.

Section 9-3

Section 9.3 Reactions in Aqueous Solutions

Double-replacement reactions occur between substances in aqueous solutions and produce precipitates, water, or gases.

Section 9-3

Section 9.3 Reactions in Aqueous Solutions (cont.)

aqueous solution

solute

solvent

complete ionic equation

spectator ion

net ionic equation

solution: a uniform mixture that might contain solids, liquids, or gases

Section 9-3

Aqueous Solutions

Aqueous Solution

contains one or more dissolved substances (called solutes) in waterSolvent

the most plentiful substance in a solution

Water is always the solvent in an aqueous solution.

Section 9-3

Aqueous Solutions (cont.)

There are many possible solutes—sugar and alcohol are molecular compounds that exist as molecules in aqueous solutions.

Compounds that produce hydrogen ions in aqueous solutions are acids.

Section 9-3

Aqueous Solutions (cont.)

Ionic compounds can also be solutes in aqueous solutions.

When ionic compounds dissolve in water, their ions separate in a process called dissociation.

Section 9-3

Types of Reactions in Aqueous Solutions

When two solutions that contain ions as solutes are combined, the ions might react.

• If they react, it is always a double replacement reaction.

• Three products can form: precipitates, water, or gases.

Section 9-3

Types of Reactions in Aqueous Solutions (cont.)

2NaOH(aq) + CuCl2(aq) → 2NaCl(aq) + Cu(OH)2(s)

Aqueous solutions of sodium hydroxide and copper(II) chloride react to form the precipitate copper(II) hydroxide.

Section 9-3

Types of Reactions in Aqueous Solutions (cont.)

Complete ionic equations

Show all of the particles in a solution as they actually exist

2Na+(aq) + 2OH–(aq) + Cu2+ (aq)+ 2Cl–(aq) → 2Na+(aq) + 2Cl–(aq) + Cu(OH)2(s)

Section 9-3

Types of Reactions in Aqueous Solutions (cont.)

Spectator Ions Ions that do not participate in a reaction and are not usually written in ionic equations.

Net Ionic Equations.

Formulas that include only the particles that participate in reactions

2OH–(aq) + Cu2+(aq) → Cu(OH)2(s)

Section 9-3

Types of Reactions in Aqueous Solutions (cont.)

Some reactions produce more water molecules.

No evidence of a chemical reaction is observable.

HBr(aq) + NaOH(aq) → H2O(l) + NaBr(aq)

Without spectator ions H+(aq) + OH–(aq) → H2O(l)

Section 9-3

Types of Reactions in Aqueous Solutions (cont.)

Gases that are commonly produced are carbon dioxide, hydrogen cyanide, and hydrogen sulfide.

2HI(aq) + Li2S(aq) → H2S(g) + 2LiI(aq)

Section 9-3

Types of Reactions in Aqueous Solutions (cont.)

Produce carbon dioxide gas mix vinegar and baking soda

HCl(aq) + NaHCO3(aq) → H2CO3(aq) + NaCl(aq)

H2CO3(aq) decomposes immediately

H2CO3(aq) → H2O(l) + CO2(g)

Section 9-3

Types of Reactions in Aqueous Solutions (cont.)

Two reactions can be combined and represented by a single chemical reaction.

Section 9-3

Types of Reactions in Aqueous Solutions (cont.)

Reaction 1

HCl(aq) + NaHCO3(aq) → H2CO3(aq) + NaCl(aq)

Reaction 2

H2CO3(aq) → H2O(l) + CO2(g)

Combined equation

HCl(aq) + NaHCO3(aq) + H2CO3(aq) → H2CO3(aq) + NaCl(aq) + H2O(l) + CO2(g)

Overall equation

HCl(aq) + NaHCO3(aq) → H2O(l) + CO2(g) + NaCl(aq)

A. A

B. B

C. C

D. D

Section 9-3

Section 9.3 Assessment

What is the solvent in an aqueous solution?

A.hydrogen

B.sodium ions

C.water

D.alcohol

A. A

B. B

C. C

D. D

Section 9-3

Section 9.3 Assessment

An equation that includes only the particles that participate in a reaction is called:

A.net ionic equation

B.spectator ions

C.complete ionic equation

D. reduced ionic equation

End of Section 9-3

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Study Guide

Chapter Assessment

Standardized Test Practice

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Study Guide 1

Section 9.1 Reactions and Equations

Key Concepts

• Some physical changes are evidence that indicate a chemical reaction has occurred.

• Word equations and skeleton equations provide important information about a chemical reaction.

• A chemical equation gives the identities and relative amounts of the reactants and products that are involved in a chemical reaction.

• Balancing an equation involves adjusting the coefficients until the number of atoms of each element is equal on both sides of the equation.

Study Guide 2

Section 9.2 Classifying Chemical Reactions

Key Concepts

• Classifying chemical reactions makes them easier to understand, remember, and recognize.

• Activity series of metals and halogens can be used to predict if single-replacement reactions will occur.

Study Guide 3

Section 9.3 Reactions in Aqueous Solutions

Key Concepts

• In aqueous solutions, the solvent is always water. There are many possible solutes.

• Many molecular compounds form ions when they dissolve in water. When some ionic compounds dissolve in water, their ions separate.

• When two aqueous solutions that contain ions as solutes are combined, the ions might react with one another. The solvent molecules do not usually react.

• Reactions that occur in aqueous solutions are double-replacement reactions.

A. A

B. B

C. C

D. D

Chapter Assessment 1

The law of conservation of mass requires what in a chemical reaction equation?

A. both sides of the equation to contain the same substances

B. the reactants to have the same amount of molecules as the products

C. both sides to have the same amount of atoms of each element

D. the products to have fewer molecules than the reactants

A. A

B. B

C. C

D. D

Chapter Assessment 2

A reaction that gives off heat is what type of reaction?

A. single replacement reaction

B. double replacement reaction

C. synthesis reaction

D. combustion reaction

A. A

B. B

C. C

D. D

Chapter Assessment 3

Ions that are present in a solution and do not participate in a chemical reaction when another substance is added are called ____.

A. spectator ions

B. reactants

C. products

D. net ions

A. A

B. B

C. C

D. D

Chapter Assessment 4

A double replacement reaction produces all of the following except ____.

A. gases

B. solids

C. light

D. water

A. A

B. B

C. C

D. D

Chapter Assessment 5

What type of reaction is the following?

2H2O(l) + energy → H2(g) + O2(g)

A. synthesis reaction

B. decomposition reaction

C. combustion reaction

D. replacement reaction

A. A

B. B

C. C

D. D

STP 1

What type of reaction is the following?

2H2(g) + O2(g) → 2H2O(l)

A. replacement reaction

B. synthesis

C. combustion reaction

D. double replacement reaction

A. A

B. B

C. C

D. D

STP 2

A precipitate forms in a double replacement reaction only if:

A. the reactivities of the compounds differ

B. the new compound is denser than water

C. the new compound is soluble in water

D. the new compound is not soluble in water

A. A

B. B

C. C

D. D

STP 3

A ____ is a statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction.

A. word equation

B. skeleton equation

C. chemical equation

D. balanced equation

A. A

B. B

C. C

D. D

STP 4

Predict the type of reaction.

LiBr2 (aq) + 2NaOH (aq) → ____

A. synthesis reaction

B. combustion reaction

C. single replacement reaction

D. double replacement reaction

A. A

B. B

C. C

D. D

STP 5

Which reactions are essentially the opposite of synthesis reactions?

A. single-replacement

B. decomposition

C. combustion

D. double-replacement

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Table 9.2 Steps for Balancing Equations

Figure 9.15 The Forming of a Precipitate

Table 9.4 Types of Chemical Reactions

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