Dinitrogen tetroxide and nitrogen dioxide are at equilibrium in a sealed flask.
N2O4(g)⇌2NO2(g) \mathrm{N_{2}O_{4}(g) \rightleftharpoons 2NO_{2}(g)} N2O4(g)⇌2NO2(g)The forward reaction is endothermic. At 10 minutes, one change is made to the flask. The graph shows the concentrations of both gases.

Which change was made at 10 minutes?
The temperature was increased.
The temperature was decreased.
A catalyst was added.
More N2O4\mathrm{N_{2}O_{4}}N2O4 was added.
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.