# Iron is used as a catalyst in the industrial production of ammonia. A student claims that using a higher temperature always improves the efficiency of an industrial process because it speeds up the reaction. Evaluate this claim in the context of a reversible reaction carried out in a closed system, referring to both the rate of reaction and the position of equilibrium.

> OCR A-Level Chemistry B: Salters (H433) — 5.3 Transition elements · Evaluate · 5 marks

> Many industrial processes use reversible reactions carried out in closed systems. The conditions chosen must balance the rate of reaction with the yield of product obtained.

## Mark scheme (5 marks)

1. Increasing temperature increases the rate of reaction because particles have more kinetic energy and collide more frequently / a greater proportion of particles have at least the activation energy
2. The student is partially correct — a higher temperature does increase the rate of reaction, so products form more quickly
3. However, in a reversible reaction at dynamic equilibrium, increasing temperature shifts the equilibrium position in the direction of the endothermic reaction
4. If the forward reaction is exothermic, increasing temperature shifts equilibrium towards the reactants, so the yield of product decreases
5. Therefore the student's claim is not fully correct — a compromise temperature is chosen to give an acceptable rate of reaction and an acceptable yield of product

## Key terms

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

## Related

- [Revision notes for OCR A-Level Chemistry B: Salters (H433)](https://www.gradenine.co.uk/learn)
- [How to answer "Evaluate" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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