Chemical Reactions
CHAPTER 9
Chemical Reactions

chemical reaction- The process by which one or more substances are
rearranged to form different substances

Evidence that a chemical reaction may have occurred:
–
Change in temperature
–
Change in color
–
Odor
–
Gas bubbles
–
Appearance of a solid
Activity

In your notebook complete the thinking map by

Identifing three examples of chemical reactions you have seen, heard, or
smelled in the last 24 hours. Think about activities at home, at school, or outside.

Depict each example

Include any evidence you have that a chemical reaction was occurring.
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.
Activity
Label the chemical state each symbol below identifies in a chemical equation.

(s) _________________________________________________________
 (g) _________________________________________________________
 (aq) _________________________________________________________

(l) __________________________________________________
Representing Chemical Reactions


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.
Representing Chemical Reactions
Chemical equation- a statement that uses chemical formulas to show the
identities and relative amounts of the substances involved in a chemical
reaction.
Activity

In your notebook on the next page
 Recreate the following table
 Organize types of equations that can express a chemical reaction.
 In the second column, list the elements (words, coefficients, etc.) that are used to create each equation.
 In the third column, rank each equation from 1 to 3, giving a 3 to the equation that provides the most
information, and a 1 to the equation that provides the least information.
Balancing Chemical Equations
This figure shows the balanced equation for the reaction between
aluminum and bromine.
Balancing Chemical Equations
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
Balancing Chemical Equations
The most fundamental law in chemistry is the law of conservation of mass.
•Balanced equations show this law.
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
Classifying Chemical Reactions
synthesis reaction
combustion reaction
decomposition reaction
single-replacement
reaction
double-replacement
reaction
precipitate
There are four types of chemical reactions:
synthesis, combustion, decomposition,
and replacement reactions.
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
two or more substances react to produce
a single product.
A + B → AB
Classifying Chemical Reactions
Types of Chemical Reactions (cont.)
When two elements react, the reaction is
always a synthesis reaction.
Classifying Chemical Reactions
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.
Classifying Chemical Reactions
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.
AB → A + B
Classifying Chemical Reactions
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
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.
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.
Classifying Chemical Reactions
Replacement Reactions (cont.)
Double replacement reactions occur
when ions exchange between two
compounds.
This figure shows a generic double
replacement equation.
Classifying Chemical Reactions
Replacement Reactions (cont.)
The solid product produced during a
chemical reaction in a solution is called a
precipitate. ANIMATION
All double replacement reactions produce
either water, a precipitate, or a gas.
Classifying Chemical Reactions
Replacement Reactions (cont.)
This table shows
the steps to
write double
replacement
reactions.
Classifying Chemical Reactions
Replacement Reactions (cont.)
This table
summarizes
different ways to
predict the
products of a
chemical reaction.
LAB

Looking at some examples of chemical reactions
QUIZ TOMORROW
Section Check
Which of the following is NOT one of the
four types of reactions?
A.
deconstructive
B.
synthesis
C.
single replacement
D.
double replacement
Section Check
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
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
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.
Reactions in Aqueous Solutions
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.
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.
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.
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.
Reactions in Aqueous Solutions
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)
Reactions in Aqueous Solutions
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)
Reactions in Aqueous Solutions
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).
Reactions in Aqueous Solutions
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)
Reactions in Aqueous Solutions
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)
Reactions in Aqueous Solutions
9
SECTION
.3
Types of Reactions in Aqueous Solutions
(cont.)
Two reactions can be combined and represented by a single chemical
reaction.
Reactions in Aqueous Solutions
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 Check
What is the solvent in an aqueous
solution?
A.
hydrogen
B.
sodium ions
C.
water
D.
alcohol
Section Check
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
Reactions and Equations
9
SECTION
.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
.2
9
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.
9
SECTION
.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 double-replacement reactions.
9
CHAPTER
Chemical Reactions
Chapter Assessment
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
9
CHAPTER
Chemical Reactions
Chapter Assessment
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
Chemical Reactions
9
CHAPTER
Chapter Assessment
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
9
CHAPTER
Chemical Reactions
Chapter Assessment
A double replacement reaction
produces all of the following except
____.
A. gases
B. solids
C. light
D. water
9
CHAPTER
Chemical Reactions
Chapter Assessment
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
9
CHAPTER
Chemical Reactions
Standardized Test Practice
What type of reaction is the following?
2H2(g) + O2(g) → 2H2O(l)
A. replacement reaction
B. synthesis
C. decomposition reaction
D. double replacement reaction
9
CHAPTER
Chemical Reactions
Standardized Test Practice
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
9
CHAPTER
Chemical Reactions
Standardized Test Practice
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
9
CHAPTER
Chemical Reactions
Standardized Test Practice
Predict the type of reaction.
LiBr2 (aq) + 2NaOH (aq) → ____
A. synthesis reaction
B. combustion reaction
C. single replacement reaction
D. double replacement reaction
9
CHAPTER
Chemical Reactions
Standardized Test Practice
Which reactions are essentially the
opposite of synthesis reactions?
A. single-replacement
B. decomposition
C. combustion
D. double-replacement