# A closed flask contains the following reversible reaction: dinitrogen tetroxide ⇌ nitrogen dioxide. At a certain temperature, the mixture reaches dynamic equilibrium. Explain what happens to the rates of the forward and backward reactions from the moment the dinitrogen tetroxide is first added to the flask until dynamic equilibrium is established.

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

> Dinitrogen tetroxide is a colourless gas. Nitrogen dioxide is a brown gas. When dinitrogen tetroxide is sealed in a flask, it begins to decompose to form nitrogen dioxide. Both gases are present in the flask at equilibrium.

## Mark scheme (4 marks)

1. Initially, only the forward reaction occurs / the rate of the forward reaction is high at the start
2. As the concentration of dinitrogen tetroxide decreases, the rate of the forward reaction decreases
3. As the concentration of nitrogen dioxide increases, the rate of the backward reaction increases
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)
- [backward reaction](https://www.gradenine.co.uk/glossary/backward-reaction)

## 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)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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