A reaction mixture reaches equilibrium in a closed container at 20 °C.
P(aq)+2Q(aq)⇌R(aq)+S(aq) \mathrm{P(aq) + 2Q(aq) \rightleftharpoons R(aq) + S(aq)} P(aq)+2Q(aq)⇌R(aq)+S(aq)The mixture is heated to 50 °C and allowed to reach a new equilibrium. Temperature is the only condition changed.
| Temperature / °C | Amount of R at equilibrium / mol |
|---|---|
| 20 | 0.040 |
| 50 | 0.027 |
Use the results to explain whether the forward reaction is exothermic or endothermic.
The mixture is cooled to 10 °C and allowed to reach equilibrium again. Predict how the amount of R at 10 °C compares with the amount at 20 °C. Explain your answer.
In a separate experiment at 20 °C, the concentration of Q is increased while the temperature and volume remain constant. Explain the effect on the position of equilibrium.
124 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.