CHEMICAL
REACTIONS
Chemistry Matter and
Change Chapter 9
Chapter 9 Big Idea
Millions of chemical
reactions in and around
you transform reactants
into products, resulting
in the absorption or
release of energy.
REACTIONS AND
EQUATIONS
Chemistry Matter
and Change
Chapter 9.1
9.1 Main Idea
Chemical reactions are
represented by balanced
chemical equations.
9.1 Objectives
• Recognize evidence of
chemical reactions
• Represent chemical
reactions with equations
• Balance chemical
equations
9.1 Review Vocabulary
and Concepts
• Chemical change
• Dalton’s atomic theory
• Law of conservation of
mass
9.1 New Vocabulary and
Concepts
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Chemical reaction
Reactant
Product
Chemical equation
Coefficient
(s), (l), (g), (aq)


Chemical reaction
• Process by which atoms are
rearranged
Evidence of chemical
reactions
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Temperature/energy change
Gas emitted (odor)
Precipitate forms
Color change
Change of substance(s)
Representing chemical
reactions
• 4+1=2+3
• Reactant + reactant  product +
product
• Need one or more reactants and one
or more products
Symbols you need to know
Symbol
Meaning
+
Plus

Yields

Reversible reaction
(s)
Solid
(l)
Liquid
(g)
Gas
(aq)
Aqueous (in water)
x


χ represents something that is needed for the reaction, but not
consumed in the reaction
Three types of equations
• Word equations
• Skeletal equations
• Chemical equations
Types of equations
Word
• Indicates
identity of
substances
involved
Skeletal
• Indicates
identity (by
molecular
formulae) of
substances
involved
Chemical
• Indicates
identity (by
molecular
formulae)
and relative
quantity of
substances
involved
Hydrogen + oxygen
 water
H2 + O2  H2O
2H2 + O2  2H2O
Balancing chemical equations
• Conservation of mass
– What goes in, must come out
– What comes out, must have gone in
Balancing equations:
1. Write out word equation
2. Write out skeletal equation
3. Balance each atom
– MINOH (aka Tarzan method)
•
Metals, ions, nonmetals, oxygen, hydrogen
– Start with “rare” elements
– Leave atoms in multiple places until last
“Me know chemistry,” said Tarzan as he
climbed the stoichiom-eh-tree.
Sample 1
• Magnesium and bromine form
magnesium bromide
– Mg + Br2  MgBr2
(balanced)
• Magnesium and oxygen form
magnesium oxide
– Mg + O2  MgO (not balanced)
– 2Mg + O2  2MgO (balanced)
Sample 2
• Nitrogen and hydrogen form
ammonia
• N2 + H2  NH3
• N2 + 3H2  2NH3
Sample 3
• Zn + HCl  ZnCl2 + H2
• Na + H2O  NaOH + H2
For you to practice
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Fe + O2  Fe2O3
Fe2O3 + H2  Fe + H2O
Sb + O2  Sb4O6
Al + HCl  AlCl3 + H2
H2O + CO2  C6H12O6 + O2
More hints
• Keep polyatomic ions together if
they appear on both sides of the
equation
• Diatomics always exist in pairs
Can you…
• Recognize evidence of chemical
reactions
• Represent chemical reactions with
equations
• Balance chemical equations
CLASSIFYING CHEMICAL
REACTIONS
Chapter 9.2
9.2 Main Idea
There are five types of
chemical reactions:
synthesis,
decomposition, single
replacement, double
replacement, and
combustion
9.2 Objectives
• Classify chemical
reactions
• Identify the
characteristics of
different classes of
chemical reactions
9.2 Review Vocabulary
and Concepts
• Metal
• Nonmetal
• precipitate
9.2 New Vocabulary and
Concepts
Synthesis reaction
Combustion reaction
Decomposition reaction
Single-replacement
reaction
• Double replacement
reaction
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5 Types of chemical reactions
1. Synthesis
2. Decomposition
3. Combustion
4. Single replacement (displacement)
5. Double replacement (displacement)
Synthesis
• E+EC
• Two or more reactants form one
product
• 2H2 + O2  2H2O
+

Decomposition
• CE+E
• One reactant breaks down into two
or more products
• 2Fe2O3  4Fe + 3O2

+
Single replacement
• C +EE +C
• One element in a compound is
replaced by another element
• Br2 + MgCl2  MgBr2 + Cl2
+

+
Double replacement
• C+CC+C
• Elements in both compounds change
partners
• Ca(OH)2+2HClCaCl2+2H2O
+

+
Combustion
• C + O2  CO2 + H2O
• A compound plus oxygen produces
an oxide and water
• 2C2H6 + 7O2  4CO2 + 6H20
Summary of reaction types
Reaction Type
Reactants
Probably Products
Generic Equation
Synthesis
Two or more
substances
One compound
A+BAB
Decomposition
One compound
Two or more
substances
ABA+B
Single replacement
A metal and a
compound
A nonmetal and a
compound
A new metal and
compound
A new nonmetal and
a compound
A+BXAX+B
Double replacement
A metal and a
compound
A new compound
and metal
AX+BYAY+BX
Combustion
Compound and
oxygen
An oxide
A+O2AO
Predict the product(s)
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NaOH+HCl 
CH4+O2 
LiCl+Br2 
Fe+O2 
H2O 
Can you…
• Classify chemical reactions
• Identify the characteristics of
different classes of chemical
reactions
REACTIONS IN
AQUEOUS SOLUTIONS
9.3
9.3 Main Idea
Double replacement
reactions occur between
substances in aqueous
solutions and produce
precipitates, water, or
gases.
9.3 Objectives
• 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
9.3 Review Vocabulary
and Concepts
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Solution
Ionic formulae
Precipitate
Ion
9.3 New Vocabulary and
Concepts
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Aqueous solution
Solute
Solvent
Complete ionic equation
Spectator ion
Net ionic equation
Aqueous solutions
• Solvent- water
• Solute- other substance(s)
– HCl(aq) is hydrochloric acid in water
Types of reactions in aqueous
solutions
• Form Gas
– Usually Double displacement
Types of reactions in aqueous
solutions
• Form Precipitate
– Usually double
replacement
• 2KI + Pb(NO3)2 
2KNO3+PbI2
Lead iodide
Types of reactions in aqueous
solutions
• Form Water
– Acid/base reactions
• Double displacement
– Also form a salt
HCl + NaOH  NaCl+ HOH
Net Ionic Reactions
• Allow you to predict the products in
a double replacement reaction
• HBr(aq)+NaOH(aq)H2O(l)+NaBr(aq)
• H+(aq) + Br-(aq) + Na + (aq) + OH-(aq) 
H2O(l) + Na+(aq)+ Br-(aq)
• H+ + OH- H2O
Writing Net Ionic Reactions
• Perchloric acid reacts with aqueous
potassium carbonate forming potassium
chlorate, carbon dioxide gas and water.
Step 1: figure out the chemical formulae and
phase for all substances
• Perchloric acid: HClO4(aq)
• Potassium carbonate: K2CO3(aq)
• Water: H2O(l)
• Carbon dioxide: CO2(g)
• Potassium perchlorate: KClO4
Writing Net Ionic Reactions
• Perchloric acid reacts with aqueous
potassium carbonate forming
potassium chlorate, carbon dioxide
gas and water.
Step 2: write the skeletal equation
HClO4(aq)+K2CO3(aq) 
H2O(l)+CO2(g)+KClO4(aq)
Writing Net Ionic Reactions
• Perchloric acid reacts with aqueous
potassium carbonate forming
potassium chlorate, carbon dioxide
gas and water.
Step 3: balance the equation
2HClO4(aq) + K2CO3(aq) 
H2O(l) +CO2(g) + 2KClO4(aq)
Writing Net Ionic Reactions
• Perchloric acid reacts with aqueous
potassium carbonate forming carbon
dioxide gas and water.
Step 4: Write the complete ionic
equation
2H+(aq) + 2ClO4-(aq) + 2K+(aq) + CO32-(aq)
 H2O(l) + CO2(g) + 2K+(aq) + 2ClO4-(aq)
Writing Net Ionic Reactions
• Perchloric acid reacts with aqueous
potassium carbonate forming carbon
dioxide gas and water.
Step 5: Cross out balanced terms
2H+(aq) + 2ClO4-(aq) + 2K+(aq) + CO32-(aq)
 H2O(l) + CO2(g) + 2K+(aq) + 2ClO4-(aq)
Writing Net Ionic Reactions
• Perchloric acid reacts with aqueous
potassium carbonate forming carbon
dioxide gas and water.
Step 6: write net ionic equation
2H+(aq) + CO32-(aq)  H2O(l) +CO2(g)
Practice
• Sulfuric acid reacts with aqueous
sodium cyanide, forming hydrogen
cyanide gas and aqueous sodium
sulfate
– You can reduce coefficients if you’d like
2H+(aq) + 2CN-(aq)  2HCN(g)
or
H+(aq) + CN-(aq)  HCN(g)
Can you…
• 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