A reversible reaction between two dissolved substances takes place in a sealed reaction cell.
P(aq)⇌Q(aq)\mathrm{P(aq) \rightleftharpoons Q(aq)}P(aq)⇌Q(aq)
At the start, the solution contains Q but no P. Its concentration of Q is 1.00 mol dm-3. The mass of the cell and its contents is 128.40 g.
The cell is kept at constant temperature. Both sets of concentration readings in each record are taken after dynamic equilibrium has been reached.
| Record | Concentration of P at 30 minutes in mol dm−3\text{mol dm}^{-3}mol dm−3 | Concentration of Q at 30 minutes in mol dm−3\text{mol dm}^{-3}mol dm−3 | Concentration of P at 40 minutes in mol dm−3\text{mol dm}^{-3}mol dm−3 | Concentration of Q at 40 minutes in mol dm−3\text{mol dm}^{-3}mol dm−3 | Mass of cell and contents at 40 minutes in g |
|---|---|---|---|---|---|
| A | 0.35 | 0.65 | 0.35 | 0.65 | 128.40 |
| B | 0.50 | 0.50 | 0.50 | 0.50 | 126.40 |
| C | 0.00 | 1.00 | 0.00 | 1.00 | 128.40 |
| D | 0.35 | 0.65 | 0.40 | 0.60 | 128.40 |
Which record could be correct?
Record C
Record D
Record B
Record A
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.