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Cracking

Chemistry: AQA A Level, topic 5.2.2

Cracking

Cracking is the process of converting alkanes into alkenes and shorter alkanes. We crack alkanes because the shorter chain alkanes are more valuable (they are used as fuel).

Thermal cracking

Thermal cracking

  • Thermal cracking uses harsh conditions like high temperature and high pressure.
  • It breaks the alkanes into a high percentage of alkenes and comparatively few alkanes.
  • Thermal cracking is done at about 1,000oC and 70 atm pressure.
Catalytic cracking

Catalytic cracking

  • Using a catalyst allows you to lower the temperatures and pressures needed for the reaction. This reduces costs and makes the reaction faster.
  • Catalytic cracking is done at 450oC and only just above atmospheric pressure.
  • The catalyst we use is called a zeolite. This is an ionic compound containing aluminium, silicon, and oxygen.
  • You tend to get molecules containing benzene rings and short hydrocarbons.

Test yourself on Cracking

  • What are the reaction conditions for catalytic cracking?

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