Combustion of Fossil Fuels

  • Non-renewable fossil fuels are obtained from crude oil by fractional distillation.
  • Petrol is used as a fuel in cars, kerosene is used to fuel aircraft and diesel oil is used as a fuel in some cars, trucks and heavy vehicles such as tanks and trains.
  • There are finite amounts of all three and they all contribute to pollution and global warming.
  • Natural gas consists mainly of methane, CH4.
  • This is also a non-renewable fuel as there are finite reserves available.

Complete & Incomplete Combustion

Complete Combustion

  • A fuel is a substance which releases energy in an exothermic reaction called combustion (burning).
  • When the fuel is a hydrocarbon then water and carbon dioxide are the products formed.
  • Hydrocarbon compounds undergo complete and incomplete combustion.
  • Complete combustion occurs when there is excess oxygen.
  • Propane for example undergoes combustion according to the following equation:

C3H8 + 5O2 → 3CO2 + 4H2O

Incomplete Combustion

  • Incomplete combustion occurs when there is insufficient oxygen to burn.
  • It occurs in some appliances such as boilers and stoves as well as in internal combustion engines, where space is cramped.
  • The products of these reactions are unburnt fuel (soot), carbon monoxide and water.
  • Methane for example undergoes incomplete combustion in an oxygen-poor environment:

2CH4+ 3O2→ 2CO + 4H2O

CH4+ O2→ C + 2H2O

Pollutants derived from Fossil Fuels

Carbon Monoxide

  • Incomplete combustion occurs when there is insufficient oxygen to burn.
  • The products of these reactions are soot, carbon monoxide and water.
  • Methane for example undergoes incomplete combustion in an oxygen-poor environment:

2CH4+ 3O2→ 2CO + 4H2O

CH4+ O2→ C + 2H2O

Sulfur Dioxide

  • SO2 is produced during the combustion of fossil fuels.
  • Sulfur impurities present in the fuels react with oxygen during combustion to produce sulfur dioxide.
  • Sulfur dioxide is also released from sulfide ores e.g: zinc blende (ZnS) in the extraction of zinc:

2ZnS + 3O2 → 2ZnO + 2SO2

Oxides of Nitrogen

  • Oxides of nitrogen are produced in the reaction of nitrogen with oxygen at high temperatures and pressure in car engines and high-temperature furnaces and as a product of bacterial action in soil.

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.