# Carbon monoxide reacts with steam in a reversible reaction: CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g). The forward reaction is exothermic. A mixture of these gases is allowed to reach equilibrium in a sealed container. Explain how each of the following changes affects the position of equilibrium and the yield of hydrogen: (i) increasing the temperature; (ii) increasing the pressure; (iii) adding more steam.

> AQA A-Level Chemistry (7405) — 3.1.6 Chemical equilibria, Le Chatelier and Kc · Explain · 5 marks

## Mark scheme (5 marks)

1. (i) Increasing temperature shifts the equilibrium to the left / in the endothermic direction
2. (i) Therefore the yield of hydrogen decreases
3. (ii) Increasing pressure has no effect on the position of equilibrium because there are equal numbers of moles of gas on both sides
4. (iii) Adding more steam shifts the equilibrium to the right / forward reaction is favoured
5. (iii) Therefore the yield of hydrogen increases

## Key terms

- [position of equilibrium](https://www.gradenine.co.uk/glossary/position-of-equilibrium)
- [yield](https://www.gradenine.co.uk/glossary/yield)
- [exothermic](https://www.gradenine.co.uk/glossary/exothermic)

## 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/carbon-monoxide-reacts-with-steam-in-c8fc616f) · Published by Druglandscape Ltd.