Substances P and Q are colourless in solution. Substance R forms a blue solution.
P(aq)+Q(aq)⇌R(aq) \mathrm{P(aq) + Q(aq) \rightleftharpoons R(aq)} P(aq)+Q(aq)⇌R(aq)A sealed tube contains P, Q and R at equilibrium. A material that absorbs only one of the substances is briefly placed in the mixture and then removed. The tube is sealed again.
The table shows the amounts of P, Q and R.
| Stage | Amount of P in mmol | Amount of Q in mmol | Amount of R in mmol |
|---|---|---|---|
| Initial equilibrium | 5.0 | 4.0 | 3.0 |
| Immediately after the material is removed | 2.0 | 4.0 | 3.0 |
| New equilibrium | 2.9 | 4.9 | 2.1 |
Use the data to explain what is observed as the mixture reaches the new equilibrium.
A second tube contains the same initial equilibrium mixture. This time, some R is removed.
State what happens to the amount of P as a new equilibrium is reached. Explain your answer.
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.