Describe the differences between catalytic cracking and steam cracking.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
1. Catalytic cracking uses a hot powdered aluminium oxide catalyst.
2. Steam cracking mixes the hydrocarbon vapour with steam.
3. Steam cracking requires a higher temperature; thermal decomposition occurs.
4. Both processes first vapourise the long‑chain hydrocarbon and produce smaller molecules, including alkenes and alkanes.
2. Steam cracking mixes the hydrocarbon vapour with steam.
3. Steam cracking requires a higher temperature; thermal decomposition occurs.
4. Both processes first vapourise the long‑chain hydrocarbon and produce smaller molecules, including alkenes and alkanes.
Examiner tips
- Use the exact terminology (e.g. "hot powdered aluminium oxide catalyst", "steam cracking"),
- Separate each point clearly to match the four marks.
- Mention the temperature difference and the role of steam.
- Show that both produce alkenes and alkanes.
Mark scheme (4 marks)
- Catalytic cracking uses a hot powdered aluminium oxide catalyst
- In steam cracking the hydrocarbon vapour is mixed with steam
- Steam cracking requires a very high temperature (higher than catalytic cracking) / thermal decomposition occurs in steam cracking
- Both methods first require the long-chain hydrocarbon to be heated to vaporise it / both produce smaller molecules including alkenes and alkanes
Key terms in this question
catalytic cracking · steam cracking · cracking
Related
- All AQA GCSE Chemistry (8462) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →