Introduction
Combustion reactions have as a product one or more compounds containing oxygen.
The term burn is used because combustion reactions also produce energy in the form of heat.
The most familiar combustion reactions are those that occur when a fuel such as petrol or natural gas burns in air.
The heat released can result in the production of light which is the flame or glow assocated with burning fuels.
Combustion reactions always have two reactants, one of which is elemental oxygen.
Recall elemental oxygen exists as the molecule O2.
The oxygen referred to in the definition of the combustion reaction is O2 molecules.
It is usual to refer to O2 molecules as oxygen (even though di-oxygen would be more explicit!).
Combustions may involve pure O2, or more commonly they involve air which is 20% oxygen.
The nitrogen molecules (N2) which are the other 80% of air do not react in combustion reactions.