A sealed flask contains only gas A at the start. At constant temperature, A reacts in the reversible reaction A(g)⇌B(g)\mathrm{A(g) \rightleftharpoons B(g)}A(g)⇌B(g). The table shows the amounts of A and B in the flask.
| Time / min | 0 | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|---|
| Amount of A / mol | 1.00 | 0.70 | 0.50 | 0.40 | 0.40 | 0.40 |
| Amount of B / mol | 0.00 | 0.30 | 0.50 | 0.60 | 0.60 | 0.60 |
At which recorded time is the mixture first at dynamic equilibrium, and why?
2 min, because the amounts of A and B are equal
3 min, because both reactions have now stopped
3 min, because the amounts of A and B stay constant
2 min, because the forward and reverse rates are equal
45 exam-style questions on Edexcel GCSE Chemistry 5.2 Reversible reactions and equilibria, covering 5.2.1 Reversible reactions and dynamic equilibrium, 5.2.2 The Haber process, and 5.2.3 Changing the position of a dynamic equilibrium. Each one has a worked solution and a mark scheme showing where the marks go.