Combustion Reaction Definition

What Is a Combustion Reaction in Chemistry?

Fire
Fire is evidence of a combustion reaction. Pexels

A combustion reaction is a type of chemical reaction where a compound and an oxidant is reacted to produce heat and a new product. The general form of a combustion reaction is the reaction between a hydrocarbon and oxygen to yield 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.

In order for a combustion reaction to begin, the activation energy for the reaction must be overcome. Often, combustion reactions are started with a match or other flame, which provides heat to initiate the reaction. Once combustion starts, enough heat may be produced to sustain it 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