A reversible reaction between two gases is represented by the equation
R(g)⇌S(g) \mathrm{R(g) \rightleftharpoons S(g)} R(g)⇌S(g)The gases are in a sealed, fixed-volume vessel maintained at constant temperature.
At 8 minutes, S is introduced through a valve. The addition immediately increases the concentration of S by 0.20 mol/dm³ without changing the concentration of R. The valve is then closed.
The table shows the concentrations of R and S.
| Time (min) | Concentration of R (mol/dm³) | Concentration of S (mol/dm³) |
|---|---|---|
| 0 | 1.00 | 0.00 |
| 2 | 0.80 | 0.20 |
| 4 | 0.65 | 0.35 |
| 6 | 0.60 | 0.40 |
| 8, before S is added | 0.60 | 0.40 |
| 8.1, immediately after S is added | 0.60 | 0.60 |
| 10 | 0.66 | 0.54 |
| 12 | 0.70 | 0.50 |
| 14 | 0.72 | 0.48 |
| 16 | 0.72 | 0.48 |
Use the results from 0 to 8 minutes to explain how the reaction reaches dynamic equilibrium.
Explain the changes in the concentrations of R and S after S is added at 8 minutes.
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.