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Science

Using carbon fuels

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Combustion - Higher tier

You should be able to write balanced symbol equations for the complete combustion - or incomplete combustion - of a simple hydrocarbon fuel, if you are given its molecular formula.

The formula of oxygen gas is O2.

The table summarises the formulas of the possible combustion products from hydrocarbon fuels.

Formulas of the possible combustion products from hydrocarbon fuels

nameformulaformed in complete combustionformed in incomplete combustion
carbon dioxideCO2yes 
carbon monoxideCO yes
sootC yes
waterH2Oyesyes

Here are some examples of how to balance symbol equations for combustion. Remember that you should have the same number of atoms of each element on each side of the arrow.

Example 1

Complete combustion of methane, CH4

Write formulae for each substance

CH4 + O2    →    CO2 + H2O

Balance the number of H atoms

CH4 + O2    →    CO2 + 2H2O

Balance the number of O atoms

CH4 + 2O2    →    CO2 + 2H2O

Example 2

Incomplete combustion of ethane, C2H6

Write formulae for each substance

C2H6 + O2    →    CO + C + H2O

Balance the number of H atoms

C2H6 + O2    →    CO + C + 3H2O

Balance the number of O atoms

C2H6 + 2O2    →    CO + C + 3H2O

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