Describe the differences between catalytic cracking and steam cracking. In your answer, include the conditions used in each process and the types of products formed.

AQA A-Level Chemistry (7405) — 3.3.15 NMR spectroscopy (A-Level only) · Describe · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (5 marks)

Catalytic cracking uses a hot powdered aluminium oxide catalyst; the feedstock is heated to vapourise it and the vapour is passed over the catalyst.
Steam cracking mixes hydrocarbon vapour with steam and heats it to a very high temperature.
Both processes break large molecules into smaller ones.
The main products are smaller alkanes.
They also produce alkenes, unsaturated hydrocarbons containing at least one C=C bond.

Examiner tips

  • Use the exact terminology: 'hot powdered aluminium oxide catalyst', 'vapourise', 'steam cracking', 'high temperature', 'smaller alkanes', 'alkenes'. Show the two processes in separate sentences to avoid mixing details. Include both product types (alkanes and alkenes) to gain full marks.
  • common_mistakes
  • :
  • Confusing catalytic cracking with non‑catalytic cracking. Omitting the use of steam in steam cracking. Failing to mention both alkanes and alkenes as products.

Mark scheme (5 marks)

  1. Catalytic cracking uses a hot powdered aluminium oxide catalyst
  2. In catalytic cracking, the hydrocarbon is heated to vaporise it / turned into a gas before passing over the catalyst
  3. Steam cracking involves mixing hydrocarbon vapour with steam and heating to a very high temperature
  4. Both processes produce smaller alkane molecules as products
  5. Both processes also produce alkenes, which are unsaturated hydrocarbons with at least one carbon-carbon double bond

Key terms in this question

catalytic cracking · steam cracking

Related

More NMR spectroscopy (A-Level only) questions

▶ Try answering this question with AI marking (free) →