Combustion of Hydrocarbons (Edexcel GCSE Chemistry)
Revision Note
Combustion of Hydrocarbons
Combustion of alkanes
Alkanes and alkenes undergo combustion in the presence of air
Complete combustion occurs to form water and carbon dioxide gas
For example, the simplest alkane, methane burns as follows:
CH4 + 2O2 → CO2 + 2H2O
Gasoline is largely composed of isomers of octane, C8H18 , which requires large amounts of oxygen to combust fully
2C8H18 + 25O2 → 16CO2 + 18H2O
The efficiency of car engines does not usually enable all the gasoline to burn, so car exhaust will contain small amounts of unburnt hydrocarbons as well as other products such as carbon monoxide and soot which lead to environmental problems
The carbon dioxide produced is a major contributor to global warming and the replacement of combustion engines with electric vehicles is a major on-going challenge for all countries
Methane, the main component of natural gas, is the fuel used in Bunsen burners which can control the degree of combustion and hotness of the flames:
Combustion of Methane in a Bunsen Burner
Combustion of alkenes
These compounds undergo complete and incomplete combustion, but because of the higher carbon to hydrogen ratio they tend to undergo incomplete combustion, producing a smoky flame in air
Complete combustion occurs when there is excess oxygen so water and carbon dioxide form e.g:
C4H8 + 6O2 → 4CO2 + 4H2O
butene + oxygen → carbon dioxide + water
Examiner Tips and Tricks
Combustion and burning are the same thing - an exothermic reaction with oxygen that produces the oxides of elements.
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