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Types of Chemical Reactions
It is important that you know the basic types of chemical
reactions for the SAT II Chemistry test since the test often refers
to reactions as being of one type or another. Here’s a list of the
different types of reactions, with examples of each type included.
Synthesis reaction: This is a reaction in
which two or more elements or compounds combine to form a single
product. This type of reaction follows the general equation
A + B
C
C where A and B may be
either elements or compounds.
Here are some examples:
2Na(s) + Cl2(g)
2NaCl(s)
2NaCl(s)MgO(s) + H2O(l)
Mg(OH)2(aq)
Mg(OH)2(aq)SO2(g) + H2O(l)
H2SO3(aq)
H2SO3(aq)Decomposition reaction: In this type of reaction,
a single reactant, a compound, breaks into two or more parts. Often
these are the most difficult to predict. Here is the general equation:
AB
A + B
A + Bwhere A and B may be
either elements or compounds.
Here are some examples of decomposition reactions:
2H2O(l)
2H2(g) + O2(g)
2H2(g) + O2(g)H2CO3(aq)
H2O(l) +
CO2(g)
H2O(l) +
CO2(g)CaCO3(s)
CaO(s) + CO2(g)
CaO(s) + CO2(g)2KClO3(s)
2KCl(s) + 3O2(g)
2KCl(s) + 3O2(g)Single replacement or displacement reaction:
In this type of reaction, a more active element replaces a less
active element in a compound. Among the halogens, F2 is
the most active halogen, and the activity of the halogens decreases
as you go down the group. For the metals, you will need to be given
an activity series. General equation:
A + BC
AC + B
AC + Bwhere A is a metal.
Here is an example of a displacement reaction in which
a metal is involved:
Cu(s) + 2AgNO3(aq)
2Ag(s) + Cu(NO3)2(aq)
2Ag(s) + Cu(NO3)2(aq)General equation:
A + BC
BA + C
BA + Cwhere A is a nonmetal.
Here is an example of a displacement reaction where a
nonmetal is involved:
Cl2(g) + 2NaI(aq)
2NaCl(aq) + I2(s)
2NaCl(aq) + I2(s)Double replacement or displacement reaction:
In this type of reaction, two compounds react to form two new compounds.
The formation of a molecular compound such as water, the formation
of a gas, or the formation of a precipitate usually drives these
reactions. Here’s the general equation:
AB + CD
AD + CB
AD + CBAnd here are a couple of examples:
Pb(NO3)2(aq) +
2KI(aq)
2KNO3(aq) +
PbI2(s)
2KNO3(aq) +
PbI2(s)HCl(aq) + NaOH(aq)
H2O(l) +
NaCl(aq)
H2O(l) +
NaCl(aq)Combustion reaction: In this type of reaction,
often a hydrocarbon is burned in the presence of oxygen gas to form
carbon dioxide (in a complete combustion) or carbon monoxide (in an
incomplete combustion, due to a limited amount of oxygen). Here
is the general equation in the presence of plenty of oxygen:
CxHy +
O2(g)
CO2(g) +
H2O(l) or (g)
CO2(g) +
H2O(l) or (g)An example of this is seen when methane gas is burned
in the presence of excess oxygen (Bunsen burner reaction):
CH4(g) + 2O2(g)
CO2(g) + 2H2O(g)
CO2(g) + 2H2O(g)Here is the general equation for when a hydrocarbon is
burned in an incomplete combustion (oxygen is in limited supply):
CxHy +
O2(g)
CO(g) +
H2O(l)
CO(g) +
H2O(l)Hydrolysis reaction: A reaction that involves
water. Here is the general equation for a hydrolysis reaction:
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