A computer model shows four reversible reactions. Each reaction takes place in a closed system.
| Model | Amount of reactant in mol | Amount of product in mol | Forward reaction rate in mol/s | Reverse reaction rate in mol/s |
|---|---|---|---|---|
| P | 0.50 | 0.50 | 0.030 | 0.012 |
| Q | 0.65 | 0.35 | 0.025 | 0.010 |
| R | 0.20 | 0.80 | 0.000 | 0.000 |
| S | 0.35 | 0.65 | 0.014 | 0.014 |
Which model represents a system at equilibrium?
Model R, because both reactions have stopped so the amounts do not change
Model Q, because the forward reaction is faster than the reverse reaction
Model P, because the amounts of reactant and product are equal
Model S, because the forward and reverse reactions occur at the same rate
109 exam-style questions on AQA GCSE Chemistry 6.2 Reversible reactions and dynamic equilibrium, covering 6.2.1 Reversible reactions, 6.2.2 Energy changes and reversible reactions, 6.2.3 Equilibrium, 6.2.4 The effect of changing conditions on equilibrium, 6.2.5 The effect of changing concentration, 6.2.6 The effect of temperature changes on equilibrium, and 6.2.7 The effect of pressure changes on equilibrium. Each one has a worked solution and a mark scheme showing where the marks go.