The Complete Combustion of Natural Gas - Methane.
Complete combustion happens when the
hydrocarbon burns in an excess of air. An excess
of air means that there is more than enough oxygen
to cause all of the carbon to turn into carbon dioxide.
The methane gas burns with a clear blue flame.
methane + oxygen 
carbon dioxide + water + energy
CH4(g) + 2O2(g) CO2(g) + 2H2O(l)
The reaction is exothermic (it gives out heat).
The heat released from burning natural gas is
used for central heating and to generate electricity.
You must know how to test for the products of combustion.
See the test for carbon dioxide and the test for water vapour.
The Complete Combustion of Ethane.
ethane + oxygen carbon dioxide + water + energy
2C2H6(g) + 7O2(g) 4CO2(g) + 6H2O(l)
The reaction is exothermic (it gives out heat).
The products are the same (carbon dioxide and water).
More oxygen is required for the complete combustion
of ethane (compared to methane above)
giving four times the quantity of carbon dioxide
and three times the quantity of water.
Combustion of hydrocarbons, whether
complete or incomplete, has environmental
and health concerns - see environmental issues.
