# Iron is produced industrially using a blast furnace. A chemist is investigating a different industrial process in which iron(III) oxide is reduced by carbon monoxide in a reversible reaction carried out in a closed system: Fe₂O₃(s) + 3CO(g) ⇌ 2Fe(s) + 3CO₂(g). The forward reaction is exothermic. Explain how increasing the temperature and increasing the pressure would each affect the position of equilibrium in this reaction.

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

> A reversible reaction reaches dynamic equilibrium when the rate of the forward reaction equals the rate of the backward reaction. Le Chatelier's principle states that if a system at equilibrium is subjected to a change, the position of equilibrium moves to counteract that change.

## Mark scheme (5 marks)

1. Increasing temperature shifts the equilibrium position in the direction of the endothermic reaction
2. This means the equilibrium shifts in the backward/reverse direction (as the forward reaction is exothermic, the backward is endothermic)
3. Increasing pressure shifts the equilibrium towards the side with fewer moles of gas
4. There are 3 moles of gas on the left (reactant side) and 3 moles of gas on the right (product side), so the number of moles of gas is equal on both sides
5. Therefore increasing pressure has no effect on the position of equilibrium

## 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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