Combustion Reaction Definition

A combustion reaction is a type of chemical reaction in which a compound and an oxidant are reacted to produce heat and a new product. The general form of a combustion reaction can be represented by the reaction between a hydrocarbon and oxygen, which yields carbon dioxide and water:

hydrocarbon + O₂ → CO₂ + H₂O

In addition to heat, it's also common (although not necessary) for a combustion reaction to release light and produce a flame. For a combustion reaction to begin, the activation energy for the reaction must be overcome. Often, combustion reactions begin with a burning match or another flame, which provides the heat needed to initiate the reaction.

Once combustion starts, enough heat might be produced to sustain the reaction until it runs out of either fuel or oxygen.

Combustion Reaction Examples

Examples of combustion reactions include:

2 H₂ + O₂ → 2H₂O + heat
CH₄ + 2 O₂ → CO₂ + 2 H₂O + heat

Other examples include lighting a match or a burning campfire.

To recognize a combustion reaction, look for oxygen in the reactant side of the equation and the release of heat on the product side. Because it isn't a chemical product, heat isn't always shown.

Sometimes the fuel molecule also contains oxygen. A common example is ethanol (grain alcohol), which has the combustion reaction:

C₂H₅OH + 3 O₂ → 2 CO₂ + 3 H₂O