A reversible reaction between dissolved substances X and Y is monitored in a closed reaction cell at constant temperature.
X(aq)⇌Y(aq) \mathrm{X(aq) \rightleftharpoons Y(aq)} X(aq)⇌Y(aq)The concentrations of X and Y are measured using sensors.
| Time (min) | Concentration of X (mol/dm³) | Concentration of Y (mol/dm³) |
|---|---|---|
| 0 | 0.80 | 0.00 |
| 3 | 0.64 | 0.16 |
| 6 | 0.54 | 0.26 |
| 9 | 0.48 | 0.32 |
| 12 | 0.45 | 0.35 |
| 15 | 0.45 | 0.35 |
| 18 | 0.45 | 0.35 |
What conclusion about the reaction is supported by the results?
At 6 min, the mixture is at equilibrium because both X and Y are present.
At 18 min, the forward and reverse reactions have both stopped.
At 12 min, the forward and reverse reactions are happening at the same rate.
At 3 min, the reverse reaction is faster than the forward reaction.
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.