Hydrocarbons and Acid Rain

A fuel is a material that is used as a source of energy. Burning is a process by which energy is released from many fuels. Nuclear fuels release energy by nuclear fission.

Fossil fuels are energy rich substances produced by the partial decay of dead organisms. The major fossil fuels are coal, oil, natural gas and peat. Coal and peat are composed mostly of carbon. Oil and gas are composed of hydrocarbons – compounds of hydrogen and carbon e.g.CH4 is methane the main component of natural gas.

Fossil fuels are non-renewable energy sources as their formation is extremely slow, much slower that the rate at which they are being used. Energy is released from fossil fuels by combustion i.e. by burning them with oxygen.

Products of Combustion of Fossil Fuels

The burning of hydrocarbon fossil fuels produces carbon dioxide and water along with the release of energy. The example below is the combustion of natural gas.

Methane + Oxygen » Carbon Dioxide + Water + Energy

CH4 + 2O2 » CO2 + 2H2O + Energy

But hydrocarbon fossil fuels are not pure hydrocarbons. These fuels also contain sulphur and nitrogen compounds. When these compounds are burned sulphur dioxide and nitrogen oxides are formed. Posionous!

Rainwater that has a pH of less than 5.5 is known as acid rain. Unpolluted rain has a pH of 5.5; it is slightly acidic. The slight acidity of rainwater is due to its reaction with carbon dioxide of the air. Rain will have a pH lower than 5.5 when it reacts with sulphur dioxide and nitrogen oxide pollutants in the air.

Water + Carbon Dioxide » Carbonic Acid

H2O + CO2 » H2CO3