Carbon, its allotropic forms and compounds burn in sufficient oxygen to give carbon dioxide and water, with the liberation of large amount of heat and light.
(i) C + O2 → CO2 + heat + light
(ii) CH4 + 2O2→ CO2 + 2H2O+ heat + light
(iii) CH3CH2OH + 3O2→ 2CO2 + 3H2O+ heat + light
If carbon or its compound are burnt in an insufficient supply of air, then incomplete combustion of carbon or its compound takes place and carbon monoxide and water vapour and some heat are produced.