On a most basic level, a combustion reaction is one where oxygen gas (O2) reacts with anything to form carbon dioxide and water. Generally, the oxygen gas reacts with a compound of carbon and hydrogen. The combustion products are always CO2 and H2O.The generic equation for a combustion reaction is: CxHy + O2 --> CO2 + H2O.
 The first step to identifying a combustion reaction is making sure that oxygen gas is one of the reactants. If there is no O2 present, then the reaction is not combustion.For example: C2H5SH + O2 --> CO2 + H2O + SO2.
O2 is reacting with a carbon-hydrogen compound so this reaction is probably a combustion reaction.
 When a combustion reaction occurs, the products will almost always contain CO2 and H2O. If both carbon dioxide and water are not products of the reaction than combustion is not occurring.For example: C2H5SH + O2 --> CO2 + H2O + SO2.
Because CO2 and H2O are both products, this reaction is an example of combustion.
 The more problems that you do, the easier it will be for you to recognize a combustion reaction when you come across it. With some practice, you’ll be able to instantly identify a combustion reaction when you see one.Example 1: CH4 + 2O2 --> CO2 + 2H2O
Example 2: C2H5OH + 3O2 --> 2CO2 + 3H2O
Learn the components of a combustion reaction.
Verify that O2 is one of the reactants.
Check that the products yield CO2 and H2O.
Practice with some examples.
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