# Methane undergoes complete combustion according to the equation: CH₄ + 2O₂ → CO₂ + 2H₂O. Explain what is meant by complete combustion and describe the products formed. Then explain why incomplete combustion of methane is considered more dangerous to human health than complete combustion.

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

> Methane is the main component of natural gas, a fossil fuel used widely for heating and cooking. When methane burns, the conditions of combustion determine which products are formed.

## Mark scheme (5 marks)

1. Complete combustion occurs when there is sufficient oxygen (supply/available)
2. The only products of complete combustion of methane are carbon dioxide and water
3. Incomplete combustion occurs when there is insufficient oxygen
4. Incomplete combustion produces carbon monoxide (CO)
5. Carbon monoxide is a toxic gas that is dangerous / harmful to humans (because it is colourless and odourless / it cannot be detected / it prevents blood carrying oxygen)

## Key terms

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

## 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/methane-undergoes-complete-combustion-according-to-b5dd39b4) · Published by Druglandscape Ltd.