# The production of hydrogen for fuel cells involves the following reversible reaction carried out in a closed system: CH₄(g) + H₂O(g) ⇌ CO(g) + 3H₂(g). This reaction is endothermic in the forward direction. A chemical engineer wants to increase the yield of hydrogen. Explain how changes in temperature and pressure would each affect the position of equilibrium and the yield of hydrogen.

> OCR A-Level Chemistry A (H432) — 5.1 Rates, equilibrium and pH · Explain · 5 marks

> Engineers optimising hydrogen production must balance the effects of temperature and pressure on the position of equilibrium. The reaction CH₄(g) + H₂O(g) ⇌ CO(g) + 3H₂(g) is endothermic in the forward direction and involves a change in the number of moles of gas.

## Mark scheme (5 marks)

1. Increasing temperature shifts the equilibrium position in the direction of the endothermic reaction (forward reaction)
2. This increases the yield of hydrogen / more hydrogen is produced
3. Decreasing pressure shifts the equilibrium position towards the side with the larger number of moles of gas
4. This is because the right-hand side has more moles of gas (4 moles) than the left-hand side (2 moles)
5. These changes are explained by Le Chatelier's principle — the equilibrium shifts to counteract the imposed change

## Key terms

- [closed system](https://www.gradenine.co.uk/glossary/closed-system)
- [reversible reaction](https://www.gradenine.co.uk/glossary/reversible-reaction)

## Related

- [Revision notes for OCR A-Level Chemistry A (H432)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/the-production-of-hydrogen-for-fuel-9581b927) · Published by Druglandscape Ltd.