# Hydrogen iodide, HI, is formed when hydrogen and iodine react together in a closed container. The reaction reaches a dynamic equilibrium. Explain what is meant by the term 'dynamic equilibrium' and describe what would happen to the position of this equilibrium if the concentration of hydrogen gas were increased.

> Edexcel GCSE Chemistry (1CH0) — 9.3 Dynamic equilibria, calculations involving volumes of gases (Chem only) · Explain · 4 marks

> Hydrogen and iodine react together reversibly according to the following equation: H₂(g) + I₂(g) ⇌ 2HI(g)

## Mark scheme (4 marks)

1. At dynamic equilibrium, the forward and reverse reactions are both still occurring (reactions have not stopped)
2. At dynamic equilibrium, the rate of the forward reaction equals the rate of the reverse reaction
3. The position of equilibrium shifts to the right / towards the products
4. This is because the system acts to reduce the increased concentration of hydrogen / opposes the change

## Key terms

- [dynamic equilibrium](https://www.gradenine.co.uk/glossary/dynamic-equilibrium)
- [concentration](https://www.gradenine.co.uk/glossary/concentration)

## Related

- [Revision notes for Edexcel GCSE Chemistry (1CH0)](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/hydrogen-iodide-hi-is-formed-when-792a9050) · Published by Druglandscape Ltd.