Complete and Incomplete Combustion

This lesson covers the combustion of hydrocarbons — both complete and incomplete — as required by the Edexcel GCSE Chemistry specification (1CH0). You need to be able to write balanced equations for complete combustion, describe the products and dangers of incomplete combustion, and explain the environmental problems caused by burning fossil fuels.

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What Is Combustion?

Combustion is the reaction of a fuel with oxygen. It is an exothermic reaction — energy is transferred to the surroundings (released as heat and light).

Hydrocarbons are widely used as fuels because they release a large amount of energy when they burn. The products of combustion depend on how much oxygen is available.

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Complete Combustion

Complete combustion occurs when a hydrocarbon burns in a plentiful supply of oxygen. The only products are:

• Carbon dioxide (CO₂)
• Water (H₂O)

Word Equation

hydrocarbon + oxygen → carbon dioxide + water

Balanced Symbol Equations

You need to be able to write and balance symbol equations for the complete combustion of hydrocarbons.

Methane:

CH₄ + 2O₂ → CO₂ + 2H₂O

Ethane:

2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O

Propane:

C₃H₈ + 5O₂ → 3CO₂ + 4H₂O