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CHEMISTRY
Matter and Change
Chapter 9: Chemical Reactions
CHAPTER
9
Table Of Contents
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
Reactions and Equations
• Recognize evidence of
chemical change.
• Represent chemical
reactions with equations.
• Balance chemical
equations.
chemical change: a
process involving one or
more substances changing
into a new substance
chemical reaction
reactant
Chemical reactions are
represented by balanced
chemical equations.
product
chemical equation
coefficient
SECTION
9.1
Reactions and Equations
Chemical Reactions
• * is called a chemical reaction.
SECTION
Reactions and Equations
9.1
Chemical Reactions (cont.)
• Evidence that a chemical reaction may
have occurred:
– *
– *
– *
– Gas bubbles
– Appearance of a solid
SECTION
9.1
Reactions and Equations
Representing Chemical Reactions
• Chemists use statements called equations to
represent chemical reactions.
• Reactants are the *.
• Products are the *.
• This table summarizes the
symbols used in chemical
equations.
SECTION
9.1
Reactions and Equations
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)
• Both word and skeleton equations lack
information about how many atoms are involved
in the reaction.
SECTION
9.1
Reactions and Equations
Representing Chemical Reactions (cont.)
• A chemical equation is a statement that uses
chemical formulas to *
SECTION
9.1
Reactions and Equations
Balancing Chemical Equations
• This figure shows the balanced equation for the
reaction between aluminum and bromine.
SECTION
9.1
Reactions and Equations
Balancing Chemical Equations (cont.)
• A coefficient in a chemical equation is the *.
SECTION
9.1
Reactions and Equations
Balancing Chemical Equations (cont.)
SECTION
9.1
Reactions and Equations
Balancing Chemical Equations (cont.)
SECTION
9.1
Reactions and Equations
Balancing Chemical Equations (cont.)
SECTION
9.1
Reactions and Equations
Balancing Chemical Equations (cont.)
• The most fundamental law in chemistry is the
law of conservation of mass.
• Balanced equations show this law.
SECTION
9.1
Reactions and Equations
Balancing Chemical Equations (cont.)
SECTION
9.2
Classifying Chemical Reactions
• Classify chemical
reactions.
• Identify the
characteristics of
different classes of
chemical reactions.
metal: an element that is a
solid at room temperature,
a good conductor of heat
and electricity, and is
generally shiny
SECTION
9.2
Classifying Chemical Reactions
synthesis reaction
combustion reaction
decomposition reaction
double-replacement
reaction
precipitate
single-replacement
reaction
There are four types of chemical reactions:
synthesis, combustion, decomposition,
and replacement reactions.
SECTION
9.2
Classifying Chemical Reactions
Types of Chemical Reactions
• Chemists classify reactions in order to
organize the many types.
• A synthesis reaction is a reaction in which *.
SECTION
9.2
Classifying Chemical Reactions
Types of Chemical Reactions (cont.)
• When two elements react, the reaction is
always a synthesis reaction.
SECTION
9.2
Classifying Chemical Reactions
Types of Chemical Reactions (cont.)
• In a combustion reaction, *
• Heated hydrogen reacts with oxygen to produce
heat and water in a combustion reaction. This is
also a synthesis reaction.
SECTION
9.2
Classifying Chemical Reactions
Decomposition Reactions
• A decomposition reaction is one in which
*.
• Decomposition reactions often require an
energy source, such as heat, light, or
electricity, to occur.
SECTION
9.2
Classifying Chemical Reactions
Replacement Reactions
• * is called a single replacement reaction.
A + BX → AX + B
SECTION
9.2
Classifying Chemical Reactions
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
Classifying Chemical Reactions
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
Classifying Chemical Reactions
Replacement Reactions (cont.)
• Double replacement reactions occur when
*.
• This figure shows a generic double replacement
equation.
SECTION
9.2
Classifying Chemical Reactions
Replacement Reactions (cont.)
• * is called a precipitate.
• All double replacement reactions produce
either water, a precipitate, or a gas.
SECTION
9.2
Classifying Chemical Reactions
Replacement Reactions (cont.)
• This table shows the steps to write double
replacement reactions.
SECTION
9.2
Classifying Chemical Reactions
Replacement Reactions (cont.)
• This table summarizes different ways to predict
the products of a chemical reaction.
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
SECTION
9.3
Reactions in Aqueous Solutions
aqueous solution
complete ionic equation
solute
spectator ion
solvent
net ionic equation
Double-replacement reactions occur
between substances in aqueous solutions
and produce precipitates, water, or gases.
SECTION
9.3
Reactions in Aqueous Solutions
Aqueous Solutions
• An aqueous solution contains one or more *
• The solvent is the *
SECTION
9.3
Reactions in Aqueous Solutions
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
Reactions in Aqueous Solutions
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
Reactions in Aqueous Solutions
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
Reactions in Aqueous Solutions
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)
• * are called complete ionic equations.
2Na+(aq) + 2OH–(aq) + Cu2+ (aq)+ 2Cl–(aq) → 2Na+(aq)
+ 2Cl–(aq) + Cu(OH)2(s)
SECTION
Reactions in Aqueous Solutions
9.3
Types of Reactions in Aqueous Solutions
(cont.)
• * are called spectator ions and are not
usually written in ionic equations.
• * are called net ionic equations.
2OH–(aq) + Cu2+(aq) → Cu(OH)2(s)
SECTION
Reactions in Aqueous Solutions
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
Reactions in Aqueous Solutions
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
Reactions in Aqueous Solutions
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)
SECTION
Reactions in Aqueous Solutions
9.3
Types of Reactions in Aqueous Solutions
(cont.)
• Two reactions can be combined and
represented by a single chemical reaction.
SECTION
Reactions in Aqueous Solutions
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)
SECTION
Reactions and Equations
9.1
Study Guide
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.
SECTION
9.2
Classifying Chemical Reactions
Study Guide
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.
SECTION
9.3
Reactions in Aqueous Solutions
Study Guide
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 doublereplacement reactions.