Alkanes undergo oxidation or combustion in excess of oxygen and produce carbon dioxide and water. This reaction is highly exothermic in nature. For example,
CH4 + 2O2 → CO2 + H2O + 890 kJ/mol
If the combustion is carried out in the presence of an insufficient supply of air or O2, then incomplete combustion takes place forming carbon monoxide instead of carbon dioxide.
2C2H6 + 5O2 + heat → 4CO + 6H2O