Explain why cracking is an important industrial process for the petrochemical industry.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Crude oil is separated by fractional distillation into fractions. However, the supply and demand of these fractions does not always match. Cracking is used to help solve this problem.
Model answer (4 marks)
Cracking is important because it breaks down large, long‑chain hydrocarbons into smaller, shorter‑chain hydrocarbons.
This is useful as there is a higher demand for short‑chain hydrocarbons such as gasoline and diesel than for the heavy fractions that are produced by distillation.
Cracking also produces alkenes, which are key monomers for the manufacture of polymers.
The process can be carried out by catalytic cracking, using a hot aluminium oxide catalyst, or by steam cracking, which uses high temperatures and steam.
This is useful as there is a higher demand for short‑chain hydrocarbons such as gasoline and diesel than for the heavy fractions that are produced by distillation.
Cracking also produces alkenes, which are key monomers for the manufacture of polymers.
The process can be carried out by catalytic cracking, using a hot aluminium oxide catalyst, or by steam cracking, which uses high temperatures and steam.
Examiner tips
- Use the word ‘breaks down’ to show the process, not just ‘breaks’.
- Mention both the demand for fuels and the production of alkenes to cover all marks.
- State the two main types of cracking to hit the final point.
Mark scheme (4 marks)
- Cracking breaks down larger/longer-chain hydrocarbons into smaller/shorter-chain hydrocarbons
- There is greater demand for shorter-chain hydrocarbons (such as fuels) than for longer-chain fractions
- Cracking produces alkenes, which are used as monomers to make polymers
- Cracking can be carried out by catalytic cracking (using a hot aluminium oxide catalyst) or by steam cracking
Key terms in this question
Related
- All OCR GCSE Chemistry A: Gateway Science (J248) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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