Combustion of Hydrocarbons (WJEC GCSE Chemistry): Revision Note

Combustion of Fuels

• Fuels are substances that react with oxygen to release energy 

• This reaction is called combustion 

  • Due to the release of energy, combustion reactions are exothermic 

• When there is plenty of oxygen for the fuel to burn in, complete combustion occurs 

• In complete combustion, all of the elements within the fuel react fully with the oxygen 

• Many fuels, such as natural gas and petrol, consist of hydrocarbons 

  • A hydrocarbon is an compound containing hydrogen and carbon atoms only 

• When the hydrocarbon undergoes complete combustion:

  • The carbon reacts with oxygen to form carbon dioxide, CO₂

  • The hydrogen reacts with oxygen to form water, H₂O

Summary table of complete combustion reactions

• You might be asked to balance chemical equations for combustion reactions

• The balanced symbol equation for the combustion of methane is:

CH₄  +   2O₂   →   CO₂   +   2H₂O  

• To balance combustion equations, balance the carbon atoms first, then the hydrogen atoms and finally the oxygen atoms 

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Combustion is the burning of a fuel in oxygen