A combustion reaction involves any fuel which can combine with oxygen to produce both carbon dioxide and water.
The general form is:
Fuel + O2 --> CO2 + HOH
To balance a combustion reaction, use this method:
Example reaction: C4H8 + O2 --> CO2 + HOH
1. Balance the number of carbon atoms on both sides using coefficients.
C4H8 + O2 --> 4 CO2 + HOH
2. Balance the number of hydrogen atoms on both sides of the equation using coefficients.
C4H8 + O2 --> 4 CO2 + 4 HOH
3. Balance the oxygen atoms. You have 8 oxygen in the CO2 + 4 in the water for a total of 12 oxygen atoms on the right. Divide the 12 by 2 ( you have two already on the left) and you get 6.
Now complete balancing:
C4H8 + 6 O2 --> 4 CO2 + 4 HOH
Here is a simple way to remember. Whenever you hear about combustion remember that three things are fixed and are bound to be formed.
Combustion, particularly that of Hydrocarbons, i.e. butene, octane etc, in a reaction, (usually involving heat) will always give a resultant product of Carbon Dioxide (CO2) and Water (H2O).