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SECTION 7–2:
TYPES OF REACTIONS
Physical Science
Coach Kelsoe
Pages 199–205
OBJECTIVES
Interpret chemical equations in terms of
reactants, products, and conservation of mass.
 Balance chemical equations by manipulating
coefficients.
 Convert between moles and mass of a substance
using molar mass.
 Calculate amounts of reactants or products by
using molar mass, mole ratios, and balanced
chemical equations.
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CLASSIFYING REACTIONS
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There are five general chemical reactions that
take place in nature:
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Synthesis
Decomposition
Single-replacement
Double-replacement
Combustion
SYNTHESIS REACTIONS
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A synthesis reaction is a reaction in which two or more
substances react to form a single substance.
The general equation for a synthesis reaction is:
A + B  AB
2H2 + O2  2H2O
Which of the following is NOT always true about a
synthesis reaction? A: There is only one reactant.
An iron fence is left unpainted, and it reacts with the
oxygen in the air, forming rust. The formation of rust is an
oxidation-reduction reaction, but it is also an example of a
synthesis reaction.
DECOMPOSITION REACTIONS
A decomposition reaction is a reaction in
which a compound breaks down into two or more
simpler substances.
 The general equation for a decomposition
reaction is
AB  A + B
2H2O  2H2 + O2
CaCO3  CaO + CO2
 A decomposition reaction is the opposite of a
synthesis reaction.
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SINGLE-REPLACEMENT REACTION
A single-replacement reaction is a reaction in
which one element takes the place of another
element in a compound.
 The general equation for a single-replacement
reaction is:
A + BC  B +AC
Cu + 2AgNO3  2Ag + Cu(NO3)2
 A cation will only replace a cation, and an anion
will only replace an anion.
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DOUBLE REPLACEMENT REACTION
A double-replacement reaction is one in
which two different compounds exchange positive
ions and form two new compounds.
 The general equation for a double-replacement
reaction is:
AB + CD  AD + CB
Pb(NO3)2 + 2KI  PbI2 + 2KNO3
 In a double-replacement reaction, there are two
reactants and two products.
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COMBUSTION REACTION
A combustion reaction is one in which a
substance reacts rapidly with oxygen, often
producing heat and light.
 Combustion reactions can also be synthesis
reactions, but don’t necessarily have to be.
 The combustion of a hydrocarbon always
produces carbon dioxide (CO2) and water (H2O).
 The element oxygen is always present in a
combustion reaction.
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TYPES OF REACTIONS
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When magnesium carbonate, MgCO2, reacts with
nitric acid, HNO3, magnesium nitrate and carbonic
acid form. Carbonic acid then breaks down into water
and carbon dioxide. Which two types of reactions
take place in this process? A: Double-replacement and
decomposition
Single-replacement reactions can take place with
nonmetals. In the following equation, assume that A
and C are nonmetals and B is a metal. Complete the
following general equation for the replacement of a
nonmetal in a compound by another nonmetal: A +
BC  C + BA.
REACTIONS AS ELECTRON TRANSFERS
The discovery of subatomic particles enabled
scientists to classify certain chemical reactions as
transfers of electrons between atoms.
 A reaction in which electrons are transferred
from one reactant to another is called an
oxidation-reduction reaction.
 Which of the following takes place during a redox
reaction? A: Electrons are both gained and lost.
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OXIDATION
Any process in which an element loses electrons
during a chemical reaction is called an oxidation.
 Oxygen is not necessary for an element to go
through oxidation. This is a broad term for losing
electrons.
 Sodium (Na) atoms go through oxidation to
become ions: Na  Na+ + 1e-. Everything in
groups 1-13 can go through oxidation.
 In a chemical reaction, an iron atom became the
ion Fe2+. What happened to the iron atom? A: It
lost electrons and was oxidized.
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REDUCTION
The process in which an element gains electrons
during a chemical reaction is called reduction.
 A reactant is said to be reduced if it gains
electrons.
 Oxidation and reduction always occur together.
When one element loses electrons, another must
gain them.
 When fluorine reacts with a metal, it forms an Fion. The fluorine atom has gained an electron
and undergone reduction.
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VOCABULARY
Synthesis reaction
 Decomposition reaction
 Single-replacement reaction
 Double-replacement reaction
 Combustion reaction
 Oxidation-reduction reaction
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STUDY GUIDE
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#13-16, 33-37 should be completed.