Combustion

The scientific name for burning is combustion. When hydrocarbons burn they combine with oxygen to produce carbon dioxide and water. The reaction releases energy.

Combustion of methane
Methane is a hydrocarbon. It is the main gas in natural gas.

meathne + oxygen = carbon dioxide + water

CH4(g)  + 202(g)   = CO2(g)            + 2H2O(l)

The methane has been oxidised. Combustion is an example of an oxidation reaction.

Complete combustion
A combustion reaction is described as complete combustion if all the hydrocarbon is oxidised and the only products are carbon dioxide and water. Complete combustion happens when there is plenty of oxygen available.

If there is not enough oxygen available, then incomplete combustion occurs.

Incomplete combustion
In complete combustion, all the carbon atoms in a hydrocarbon are oxidised to form carbon dioxide. All the hydrogen atoms that were in the hydrocarbon are oxidised to form water.

Sometimes there is not enough oxygen available to allow all these oxidation reactions to take place. When incomplete combustion takes place all the hydrogen atoms become oxidised to form water, but the carbon atoms may form: methane + oxygen = carbon dioxide + carbon monoxide + carbon + water
 * some carbon dioxide (CO2)
 * some carbon monoxide (CO)
 * some soot (particles of solid carbon).

Different amounts of these substances are produced, depending on how much oxygen is available. Incomplete combustion reactions release energy.