# The manufacture of ammonia uses the Haber process, which involves the following reversible reaction:

N₂(g) + 3H₂(g) ⇌ 2NH₃(g)     ΔH = −92 kJ/mol

A student claims that using a very high temperature will always give the best yield of ammonia. Evaluate this claim, using Le Chatelier's principle where appropriate.

> Edexcel A-Level Chemistry (9CH0) — 10.1 Dynamic equilibria and Le Chatelier · Evaluate · 5 marks

> The Haber process is a major industrial reaction used to produce ammonia for fertilisers and other chemicals. The reaction reaches a dynamic equilibrium under industrial conditions.

## Mark scheme (5 marks)

1. The reaction is exothermic (forward reaction releases heat / ΔH is negative)
2. By Le Chatelier's principle, increasing temperature shifts the equilibrium in the endothermic direction (reverse reaction), reducing the yield of ammonia
3. The student's claim is therefore incorrect regarding yield — a lower temperature gives a higher equilibrium yield of ammonia
4. However, a very low temperature makes the rate of reaction too slow (and the reaction would take too long to reach equilibrium)
5. A compromise / moderate temperature (around 450 °C) is used industrially to balance an acceptable rate with a reasonable yield

## Key terms

- [Le Chatelier's principle](https://www.gradenine.co.uk/glossary/le-chatelier-s-principle)
- [yield](https://www.gradenine.co.uk/glossary/yield)

## Related

- [Revision notes for Edexcel A-Level Chemistry (9CH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Evaluate" 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/the-manufacture-of-ammonia-uses-the-224791b8) · Published by Druglandscape Ltd.