# Petrol is a hydrocarbon fuel obtained from crude oil by fractional distillation. When petrol undergoes incomplete combustion in a car engine, pollutants are released into the atmosphere. Explain why incomplete combustion occurs in a car engine and describe the environmental and health problems caused by the pollutants produced during incomplete combustion.

> Edexcel A-Level Chemistry (9CH0) — 8.1 Enthalpy changes and Hess cycles · Explain · 5 marks

> Petrol is a non-renewable fossil fuel used widely in car engines. The conditions inside a car engine mean that combustion is not always complete.

## Mark scheme (5 marks)

1. Incomplete combustion occurs because there is insufficient oxygen (inside the car engine)
2. Carbon monoxide is produced as a pollutant
3. Carbon monoxide is toxic / poisonous (to humans)
4. Carbon particulates (soot) are produced as a pollutant
5. Carbon particulates cause global dimming OR cause health problems such as respiratory problems in humans

## Key terms

- [incomplete combustion](https://www.gradenine.co.uk/glossary/incomplete-combustion)
- [pollutants](https://www.gradenine.co.uk/glossary/pollutants)

## Related

- [Revision notes for Edexcel A-Level Chemistry (9CH0)](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/petrol-is-a-hydrocarbon-fuel-obtained-4d5db57d) · Published by Druglandscape Ltd.