# Explain why cracking is carried out in industry. In your answer, refer to the feedstock used, the conditions required, and the products formed.

> AQA A-Level Chemistry (7405) — 3.3.7 Optical isomerism (A-Level only) · Explain · 5 marks

## Mark scheme (5 marks)

1. Long-chain hydrocarbons / large molecules are used as the feedstock (accept: heavy fractions from crude oil)
2. There is greater demand for shorter-chain fractions / smaller molecules than supply from fractional distillation (accept: long-chain molecules are less useful / less in demand)
3. High temperature is required / hydrocarbons are heated to vaporise them (accept: catalytic cracking uses a hot powdered aluminium oxide catalyst; steam cracking uses steam and very high temperature)
4. Products include shorter-chain alkanes, which are more useful as fuels (accept: more flammable than longer-chain alkanes)
5. Alkenes are also produced, which are used to make polymers / other chemicals (accept: alkenes have a C=C double bond making them reactive / useful as monomers)

## Key terms

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

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-cracking-is-carried-out-5daf2ae3) · Published by Druglandscape Ltd.