Nitrogen dioxide, NO2\mathrm{NO_{2}}NO2, is a brown gas. Dinitrogen tetroxide, N2O4\mathrm{N_{2}O_{4}}N2O4, is a colourless gas.
The two gases take part in a reversible reaction.
2NO2(g)⇌N2O4(g) \mathrm{2NO_{2}(g) \rightleftharpoons N_{2}O_{4}(g)} 2NO2(g)⇌N2O4(g)A teacher has a sealed glass tube that contains a mixture of the two gases.
The teacher puts the tube into water baths at different temperatures, one after the other. The tube is left in each water bath for 5 minutes.
In each water bath, the colour of the gas changes during the first minute and then stays the same.
The table shows the results.
| Step | Temperature of water bath (°C) | Colour of the gas after 5 minutes |
|---|---|---|
| 1 | 20 | brown |
| 2 | 80 | dark brown |
| 3 | 20 | brown |
| 4 | 0 | pale brown |
| 5 | 20 | brown |
Give one reason why the gases are kept in a sealed tube.
Describe and explain the teacher's observations.
Use ideas about reversible reactions, closed systems and dynamic equilibrium.
47 exam-style questions on OCR GCSE Chemistry 5.3 Equilibria, covering 5.3.1 Reversible reactions and dynamic equilibrium and 5.3.2 Changing the position of equilibrium. Each one has a worked solution and a mark scheme showing where the marks go.