chemistry: matter and change chem - ch 9.pdfchemical change. chemical change: a process involving...

Chapter Menu

Chemical Reactions

Section 9.1 Reactions and

Equations

Section 9.2 Classifying Chemical

Reactions

Section 9.3 Reactions in Aqueous

Solutions

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the corresponding slides.

Section 9-1

Section 9.1 Reactions and Equations

• Recognize evidence of chemical change.

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

chemical reaction

reactant

product

chemical equation

coefficient

• Represent chemical reactions with equations.

• Balance chemical equations.

Chemical reactions are represented by balanced chemical equations.

Section 9-1

Chemical Reactions

• The process by which one or more substances are rearranged to form different substances is called a chemical reaction.

• All chemical reactions are the result of chemical changes.

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Section 9-1

Chemical Reactions (cont.)

• Evidence of a chemical reaction

– Change in temperature Ex: wood burning

– Change in color Ex: leaves changing colors

– Odor forms Ex: rotting garbage

– Gas or solid forms Ex: sour milk

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Section 9-1

Representing Chemical Reactions

• Chemists use statements called equations to represent chemical reactions.

• Reactants are the starting substances.

• Products are the substances formed in the reaction.

Section 9-1

Representing Chemical Reactions (cont.)

• Skeleton equations use symbols and formulas to represent the reactants and products. Al(s) + Br 2 (l) → AlBr3(s)

• Skeleton equations lack information about how many atoms are involved in the reaction.

Section 9-1

Representing Chemical Reactions (cont.)

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

Section 9-1

Balancing Chemical Equations

• Coefficients are used to balance chemical equations.

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

2 H2 (g) + O2 (g) 2 H2O(l)

Hints for Balancing Chemical Equations

• Count atoms of reactants & products

• Never change or alter subscripts

• Add coefficients to balance # of atoms

• Balance H and O last!!!

• Check that coefficients are in lowest ratio!!!

Balancing Chemical Equations (cont.)

Section 9-1

Balancing Chemical Equations

• This figure shows the balanced equation for the reaction between aluminum and bromine.

Section 9-1

Balancing Chemical Equations (cont.)

Why Balance Chemical Equations???

• The most fundamental law in chemistry is the law of conservation of mass.

• Balanced equations show this law!!!

A. A

B. B

C. C

D. D

Section 9-1

A B C D

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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

A B C D

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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.

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

• Identify the

characteristics of

different classes of

chemical reactions.

Section 9-2

Section 9.2 Classifying Chemical Reactions (cont.)

synthesis reaction

combustion reaction

decomposition reaction

single-replacement reaction

There are four types of chemical reactions: synthesis, combustion, decomposition, and replacement reactions.

double-replacement reaction

precipitate

Section 9-2

Types of Chemical Reactions

• Chemists classify reactions in order to organize the many types.

1. A synthesis reaction is a reaction in which two or more substances react to produce a single product.

A + B AB

Section 9-2

Types of Chemical Reactions (cont.)

• When two elements react, the reaction is always a synthesis reaction.

Section 9-2

Types of Chemical Reactions (cont.)

2. In a combustion reaction, oxygen combines with a substance and releases energy in the form of heat and light.

• Heated hydrogen reacts with oxygen to produce heat and water in a combustion reaction. This is also a synthesis reaction.

Section 9-2

Decomposition Reactions

3. A decomposition reaction is one in which a single compound breaks down into two or more elements or new compounds.

AB A + B

• Decomposition reactions often require an energy source, such as heat, light, or electricity, to occur.

Section 9-2

Replacement Reactions

4. A reaction in which the atoms of one element replace the atoms of another element in a compound is called a single replacement reaction.

A + BX → AX + B

• A metal will replace a less active metal.

• A nonmetal will replace a less active nonmetal.

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


• Halogens frequently replace other halogens in replacement reactions.

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

Section 9-2


5. Double replacement reactions occur when ions exchange between two compounds.

• The anions trade places to form new compounds.

Section 9-2


• The solid product produced during a chemical reaction in a solution is called a precipitate.

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

Section 9-2


• This table shows the steps to write double replacement reactions.

Section 9-2


• This table summarizes different ways to predict the products of a chemical reaction.

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A. A

B. B

C. C

D. D

Section 9-2

A B C D

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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


A B C D

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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.

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

• 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


(cont.)

aqueous solution

solute

solvent

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

complete ionic equation

spectator ion

net ionic equation

Section 9-3

Aqueous Solutions

• An aqueous solution contains one or more dissolved substances (called solutes) in water.

• The solvent is the most plentiful substance in a solution.

Section 9-3

Aqueous Solutions (cont.)

• Water is always the solvent in an aqueous solution.

• 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.)

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

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

• Ionic equations that show all of the particles in a solution as they actually exist are called complete ionic equations.

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

Section 9-3


• Ions that do not participate in a reaction are called spectator ions and are not usually written in ionic equations.

• Formulas that include only the particles that participate in reactions are called net ionic equations.

2OH–(aq) + Cu2+(aq) → Cu(OH)2(s)

Section 9-3


• 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


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

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

Section 9-3


• Another example is mixing vinegar and baking soda, which produces carbon dioxide gas.

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

• H2CO3(aq) decomposes immediately.

H2CO3(aq) → H2O(l) + CO2(g)

Section 9-3


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

Section 9-3


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

A B C D

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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


A B C D

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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

Resources Menu

Chemistry Online

Study Guide

Chapter Assessment

Standardized Test Practice

Image Bank

Concepts in Motion

http://www.glencoe.com/

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


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

A B C D

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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


A B C D

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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


A B C D

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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


A B C D

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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


A B C D

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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

A B C D

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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 B C D

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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 B C D

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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

A B C D

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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

A B C D

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Which reactions are essentially the opposite of synthesis reactions?

A. single-replacement

B. decomposition

C. combustion

D. double-replacement

IB Menu

Click on an image to enlarge.

CIM

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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