Combustion of Hydrocarbons (Edexcel GCSE Chemistry)

Revision Note

Stewart Hird

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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

Bunsen Burner table, IGCSE & GCSE Chemistry revision notes

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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Stewart Hird

Author: Stewart Hird

Expertise: Chemistry Lead

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Topic Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.