# The Haber process makes ammonia using the reversible reaction: N₂(g) + 3H₂(g) ⇌ 2NH₃(g). The forward reaction is exothermic. In industry, a temperature of around 450 °C and a pressure of around 200 atmospheres are used, along with an iron catalyst. Explain how each of these three conditions affects the rate of reaction and/or the position of equilibrium, and why a compromise temperature is chosen rather than a very low temperature.

> OCR A-Level Chemistry A (H432) — 5.3 Transition elements · Explain · 5 marks

> The Haber process is used industrially to manufacture ammonia on a large scale. The reaction is carried out in a closed system so that dynamic equilibrium can be established.

## Mark scheme (5 marks)

1. The iron catalyst increases the rate of reaction by providing a different reaction pathway with a lower activation energy
2. High pressure increases the rate of reaction because gaseous particles are closer together, leading to more frequent successful collisions
3. High pressure shifts the equilibrium position towards the side with the smaller number of moles of gas, i.e. towards the products / towards ammonia (4 moles → 2 moles)
4. A low temperature would shift the equilibrium position in the direction of the exothermic reaction (towards ammonia / to the right), giving a greater yield of ammonia
5. A very low temperature would make the rate of reaction too slow, so a compromise temperature of around 450 °C is used to give an acceptable rate of reaction whilst still producing a reasonable yield

## Key terms

- [catalyst](https://www.gradenine.co.uk/glossary/catalyst)
- [rate of reaction](https://www.gradenine.co.uk/glossary/rate-of-reaction)

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- [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-haber-process-makes-ammonia-using-2c10667a) · Published by Druglandscape Ltd.