When burning occurs, a number of irreversible reactions and changes take place. Most of these changes are chemical changes and are dependant on the presence of three things:
- fuel: these vary chemically in their nature but all contain sufficient levels of chemical potential energy. When burning occurs, they combine with the oxygen, and energy is transferred out from the fuel as both heat and light.
- oxygen: oxygen combines with the carbon content of the fuel (most fossil fuels are mostly carbon and hydrogen) to produce carbon dioxide.
- heat: this is required to start the burning process. Most fuels have a temperature at which burning will begin, and heat is required to get the fuel to that temperature so that the burning reaction can begin. Once started, some of the heat energy from the burning fuel will be used to heat more fuel causing the reactions to continue.
