Chemistry: Matter and Change

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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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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

• Represent chemical reactions with equations.
• Balance chemical equations.

chemical reaction reactant product chemical
equation coefficient
Chemical reactions are represented by balanced
chemical equations.
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Section 9-1
Chemical Reactions

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

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Section 9-1
Chemical Reactions (cont.)

• Evidence of a chemical reaction

• Change in temperature
• Change in color
• Odor, gas, or bubbles may form.

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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.
• This table summarizes the symbols used in
  chemical equations.

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Section 9-1
Representing Chemical Reactions (cont.)

• In word equations, aluminum(s) bromine(l) ?
  aluminum bromide(s) reads as aluminum and
  bromine react to produce aluminum bromide.

• Skeleton equations use symbols and formulas to
  represent the reactants and products. Al(s)
  Br(l) ? AlBr3(s)
• Skeleton equations lack information about how
  many atoms are involved in the reaction.

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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.

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Section 9-1
Balancing Chemical Equations

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

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Section 9-1
Balancing Chemical Equations (cont.)

• A coefficient in a chemical equation is the
  number written in front of a reactant or product,
  describing the lowest whole-number ratio of the
  amounts of all the reactants and products.

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Section 9-1
Balancing Chemical Equations (cont.)
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Section 9-1
Balancing Chemical Equations (cont.)
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Section 9-1
Balancing Chemical Equations (cont.)
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Section 9-1
Balancing Chemical Equations (cont.)

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

• Balanced equations show this law.

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Section 9-1
Balancing Chemical Equations (cont.)
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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

1. A
2. B
3. C
4. D

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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

1. A
2. B
3. C
4. D

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End of Section 9-1
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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.

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Section 9-2
Section 9.2 Classifying Chemical Reactions
(cont.)
synthesis reaction combustion reaction decompositi
on reaction single-replacement reaction
double-replacement reaction precipitate
There are four types of chemical reactions
synthesis, combustion, decomposition, and
replacement reactions.
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Section 9-2
Types of Chemical Reactions

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

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

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Section 9-2
Types of Chemical Reactions (cont.)

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

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Section 9-2
Types of Chemical Reactions (cont.)

• 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.

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Section 9-2
Decomposition Reactions

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

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

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Section 9-2
Replacement Reactions

• 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

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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.

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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.

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Section 9-2
Replacement Reactions (cont.)

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

• This figure shows a generic double replacement
  equation.

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Section 9-2
Replacement Reactions (cont.)

• 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.

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Section 9-2
Replacement Reactions (cont.)

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

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Section 9-2
Replacement Reactions (cont.)

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

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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

1. A
2. B
3. C
4. D

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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

1. A
2. B
3. C
4. D

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End of Section 9-2
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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.

solution a uniform mixture that might contain
solids, liquids, or gases
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Section 9-3
Section 9.3 Reactions in Aqueous Solutions
(cont.)
aqueous solution solute solvent
complete ionic equation spectator ion net ionic
equation
Double-replacement reactions occur between
substances in aqueous solutions and produce
precipitates, water, or gases.
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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.

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Section 9-3
Aqueous Solutions (cont.)

• Water is always the solvent in an aqueous
  solution.

• There are many possible solutessugar and alcohol
  are molecular compounds that exist as molecules
  in aqueous solutions.
• Compounds that produce hydrogen ions in aqueous
  solutions are acids.

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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.

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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.

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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)

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Section 9-3
Types of Reactions in Aqueous Solutions (cont.)

• 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)

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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).

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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)

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Section 9-3
Types of Reactions in Aqueous Solutions (cont.)

• 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)

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Section 9-3
Types of Reactions in Aqueous Solutions (cont.)

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

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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)
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Section 9-3
Section 9.3 Assessment
What is the solvent in an aqueous solution?
A. hydrogen B. sodium ions C. water
D. alcohol

1. A
2. B
3. C
4. D

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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

1. A
2. B
3. C
4. D

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End of Section 9-3
51
Resources Menu
Chemistry Online Study Guide Chapter
Assessment Standardized Test Practice Image
Bank Concepts in Motion
52
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.

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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.

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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.

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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

1. A
2. B
3. C
4. D

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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

1. A
2. B
3. C
4. D

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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

1. A
2. B
3. C
4. D

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Chapter Assessment 4
A double replacement reaction produces all of the
following except ____. A. gases B. solids
C. light D. water

1. A
2. B
3. C
4. D

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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

1. A
2. B
3. C
4. D

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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

1. A
2. B
3. C
4. D

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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

1. A
2. B
3. C
4. D

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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

1. A
2. B
3. C
4. D

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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

1. A
2. B
3. C
4. D

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STP 5
Which reactions are essentially the opposite of
synthesis reactions? A. single-replacement
B. decomposition C. combustion D. double-replace
ment

1. A
2. B
3. C
4. D

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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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