1. Classifying Chemical Reactions
There are 5 types of Chemical Reactions:
Synthesis (Combination)
Decomposition
Combustion
Single Displacement (Replacement)
Double Displacement

2. 1. Synthesis (Combination) - S
A reaction in which two or more substances combine to form a new compound.
A + B  AB
1) Two elements form a binary compound (2 elements)
C + O2  CO2
2C + O2 2CO
2) Two compounds form a ternary compound (3 elements)
CaO(s) + H2O(l)  Ca(OH)2(s)
CO2(g) + H2O(l)  H2CO3(aq)

3. 2. Decomposition - D
A reaction in which a single compound breaks down into two or more simpler substances.
AB  A + B
Decomposition of water
A metal carbonate decomposes to form a metal oxide and carbon dioxide.
electricity
2H2O(l)
O2(g) + 2H2(g)
heat
CaCO3(s)
CaO(s) + CO2(g)

4. 3. Combustion - C
A reaction in which reactants are hydrocarbon (C and H) with oxygen, and the products are carbon dioxide and water vapor.
A + O2  CO2 + H2O
Combustion of propane:
C3H8 + 5O2  3CO2 + 4H2O
Combustion of ethanol:
CH3CH2OH + 3O2  2CO2 + 3H2O

5. 4. Single Displacement - SD
A reaction in which a single element reacts with a compound and displaces another element from the compound.
AB + C  AC + B
Aluminum displaces copper
2Al(s) + 3CuCl2(aq)  2AlCl3(aq) + 3Cu(s)

6. 5. Double Displacement - DD
A reaction in which a gas, a solid precipitate, or a molecular compound forms from the apparent exchange of atoms or ions between two compounds.
AB + CD  AD + CB
HCl(aq) + NaOH(aq)  HOH(l) + NaCl(aq)
Water (HOH) is the molecular compound