Chemical Reactions
(1) Composition Reactions (also known as combination reactions or synthesis
reactions) – In a composition reaction, two or more reactants combine to
form one product.
General Pattern: A + B  AB
A and B are elements or compounds; AB is a compound
Balance the following composition equations:
Mg + O2  MgO
C + O2  CO2
K + S  K2S
(2) Decomposition Reactions – In a decomposition reaction a substance is
broken down into two or more simpler substances.
General Pattern: AB  A + B
AB is a compound; A and B are compounds or elements
Balance the following decomposition equations:
HgO 
Ag2O 
Ca(OH)2 
Fe2(SO4)3 
Hg + O2
Ag + O2
CaO + H2O
Fe2O3 + SO3
Special Decomposition Reactions
(i) Decomposition of a chlorate compounds yields a chloride compound plus
oxygen gas:
Ex. 2KClO3  2KCl + 3O2
(ii) Decomposition of a nitrate compound yields a nitrite compound plus
oxygen gas:
Ex. 2KNO3  2KNO2 + O2
(iii)
Decomposition of a carbonate compound yields an oxide compound
plus carbon dioxide:
Ex. K2CO3  K2O + CO2
Write the balanced equation for the decomposition of:
(a) sodium chlorate
(b) magnesium nitrate
(c) calcium carbonate
(3) Single displacement or single replacement reactions – In this type of
reaction, one element displaces another in a compound. This happens in
two situations:
General Pattern: A + BC  AC + B if A is a metal
Or: A + BC  BA + C if A is a non-metal
(i)
When a metal displaces a metal
Ex. Li + NaCl  LiCl + Na
(ii)
When a non-metal displaces a non-metal
Ex. F2 + 2KI  I2 + 2KF
Write the equation for copper reacting with silver nitrate (assume copper (II)):
Write the equation for lithium reacting with hydrogen hydroxide
(4) Double displacement or double replacement reactions – In a double
replacement reaction, two ionic compounds switch cations
General Pattern: AB + CD  AD + CB
Example: (NH4)2S + FeSO4  FeS + (NH4)2SO4
Na2CO3 (aq) + 2HCl  2NaCl (aq) + H2CO3 (aq)
This decomposes to give
H2O + CO2
(5) Hydrocarbon burning or combustion reaction – Almost all organic
compounds will burn in air. When an organic compound burns in air, it is
reacting with the oxygen in the air. The products under normal conditions
are carbon dioxide and water. This is called complete combustion.
Balance the following complete combustion equations:
CH4 + O2  CO2 + H2O
C4H10 + O2  CO2 + H2O
C6H12O6 + O2  CO2 + H2O
If incomplete combustion takes place, the products are carbon monoxide
and water.
Balance the following incomplete combustion equation:
C3H8 + O2  CO + H2O
CH4 + O2  CO + H2O