• The combustion of fossil fuels is the major source of atmospheric pollution
• Fossil fuels include:?coal,?oil,?natural gas,?oil shales?and tar sands
• 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
• Coal is used in power stations and also steel production
• Natural gas consists mainly of?methane, CH₄
• There are finite amounts of fossil fuels and they all contribute to?pollution?and?global?warming
• All these fuels contain carbon, hydrogen and small quantities of sulfur

Combustion Products

• The burning of fossil fuels releases the gases?carbon dioxide,?carbon monoxide,?oxides of nitrogen?and?oxides of sulfur
• In addition incomplete combustion of the fuels gives rise to?unburned hydrocarbons?and?carbon particulates

Complete versus Incomplete Combustion

• A?fuel?is a substance which releases energy in an exothermic reaction
• 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
• For example, the combustion equation for propane is:

C₃H_8?+ 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
• The products of these reactions are unburnt fuel (soot), carbon monoxide and water
• Methane for example undergoes incomplete combustion in an oxygen-poor environment:

2CH_4?+ 3O₂→ 2CO + 4H₂O

CH_4?+ O₂→ C + 2H₂O

• Carbon monoxide is a toxic and odourless gas which can cause dizziness, loss of consciousness and eventually death
  • The CO binds well to haemoglobin which therefore cannot bind oxygen and carbon dioxide
  • Oxygen is transported to organs
  • Carbon dioxide is removed as waste material from organs

   

The high affinity of CO to haemoglobin prevents it from binding to O₂?and CO₂