# Explain why cracking is carried out in the petrochemical industry, and describe the conditions used in catalytic cracking.

> AQA A-Level Chemistry (7405) — 3.3.16 Chromatography (A-Level only) · Explain · 5 marks

> Crude oil contains many long-chain hydrocarbons. There is a greater demand for shorter-chain hydrocarbons than for longer-chain ones.

## Mark scheme (5 marks)

1. There is greater demand for shorter-chain hydrocarbons / shorter-chain fractions than are produced by fractional distillation
2. Cracking breaks down larger/longer-chain hydrocarbons into smaller/shorter-chain molecules
3. Products of cracking include alkenes, which are used to make polymers / other useful chemicals
4. In catalytic cracking, the long-chain hydrocarbon is heated to vaporise it
5. The vapour is passed over a hot powdered aluminium oxide catalyst

## Key terms

- [cracking](https://www.gradenine.co.uk/glossary/cracking)
- [catalytic cracking](https://www.gradenine.co.uk/glossary/catalytic-cracking)

## Related

- [Revision notes for AQA A-Level Chemistry (7405)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-cracking-is-carried-out-b66215d4) · Published by Druglandscape Ltd.