# Describe what is meant by a reversible reaction and explain how a reversible reaction carried out in a closed system eventually reaches dynamic equilibrium.

> Edexcel GCSE Chemistry (1CH0) — 4.2 Reversible reactions and equilibria · Describe and Explain · 4 marks

> Some chemical reactions can proceed in both the forward and backward directions. When such a reaction is carried out in a closed system, a special condition known as dynamic equilibrium can be established.

## Mark scheme (4 marks)

1. A reversible reaction is one in which the products can react together to reform the reactants.
2. At the start, only the forward reaction occurs (or the forward reaction is faster than the backward reaction), so the concentration of products increases.
3. As products build up, the rate of the backward reaction increases (and the rate of the forward reaction decreases).
4. Dynamic equilibrium is reached when the rate of the forward reaction equals the rate of the backward reaction, so the concentrations of reactants and products remain constant.

## Key terms

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

## Related

- [Revision notes for Edexcel GCSE Chemistry (1CH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and 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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