# Nitrogen and hydrogen react together in a reversible reaction to form ammonia: N₂(g) + 3H₂(g) ⇌ 2NH₃(g). The forward reaction is exothermic. Explain how each of the following changes would affect the position of equilibrium and the yield of ammonia: increasing the pressure; increasing the temperature.

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

## Mark scheme (5 marks)

1. Increasing pressure shifts the equilibrium to the right / towards the side with fewer moles of gas
2. Because there are 4 moles of gas on the left and 2 moles of gas on the right, so the reaction that produces fewer moles of gas is favoured
3. Increasing pressure increases the yield of ammonia
4. Increasing temperature shifts the equilibrium to the left / in the endothermic direction
5. Because the forward reaction is exothermic, the system opposes the increase in temperature by favouring the endothermic (reverse) reaction, so the yield of ammonia decreases

## Key terms

- [reversible reaction](https://www.gradenine.co.uk/glossary/reversible-reaction)
- [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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/nitrogen-and-hydrogen-react-together-in-49268843) · Published by Druglandscape Ltd.