Carbon and its compounds are used as fuels because they burn in air releasing a lot of heat energy. For example:
(i) When carbon (in the form of coal) is burned in air, it forms carbon dioxide gas and releases a lot of heat:
`underset(("Coal"))underset("Carbon")(C)+underset(("From air"))underset("Oxygen")(O_(2))overset("Burning")(to)underset("Carbon dioxide")(CO_(2))+"Heat"`
(ii) When a carbon compound methane (in the form of natural gas) is burned in air, it forms carbon dioxide and water vapour, and releases a lot of heat:
`underset(("Natural gas"))underset("Methane")(CH_(4))+underset(("From air"))underset("Oxygen")(2O_(2))overset("Burning")(to) underset("Carbon dioxide")(CO_(2))+underset("Water")(2H_(2)O)+"Heat"`
