# Sulfur dioxide reacts with oxygen to form sulfur trioxide in a reversible reaction: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g). The forward reaction is exothermic. Explain what happens to the position of equilibrium and the yield of sulfur trioxide when the temperature is increased.

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

## Mark scheme (5 marks)

1. The position of equilibrium shifts to the left (reverse reaction is favoured)
2. This is because increasing temperature favours the endothermic reaction / the system opposes the change by absorbing the extra heat energy
3. The yield / amount of sulfur trioxide decreases
4. The reverse reaction converts sulfur trioxide back into sulfur dioxide and oxygen
5. The reaction is reversible / a dynamic equilibrium is established, so the equilibrium position changes but both forward and reverse reactions still occur

## Key terms

- [reversible reaction](https://www.gradenine.co.uk/glossary/reversible-reaction)
- [position of equilibrium](https://www.gradenine.co.uk/glossary/position-of-equilibrium)
- [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)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/sulfur-dioxide-reacts-with-oxygen-to-3c3162e4) · Published by Druglandscape Ltd.