A dimer, Q, is stable when solid but a dynamic equilibrium is set up in solution.

Q(aq) ⇌ 2R(aq)

A solution of Q has an initial concentration of 0.50 mol dm⁻³. When equilibrium has been reached, [Q(aq)] has fallen to 0.25 mol dm⁻³.

The changes in [Q(aq)] and [R(aq)] are plotted against time until equilibrium is reached. The value of Kc is then calculated.

Which graph and value for Kc are correct?

This question tests Equilibria in A-Level Chemistry (syllabus code 9701). It is worth 1 mark.

This question appeared in the Cambridge A-Level Chemistry Oct/Nov 2022 examination, Paper 1 Variant 2 (9701_w22_qp_12.pdf).

Question

A dimer, Q, is stable when solid but a dynamic equilibrium is set up in solution.

Q(aq) ⇌ 2R(aq)

A solution of Q has an initial concentration of 0.50 mol dm⁻³. When equilibrium has been reached, [Q(aq)] has fallen to 0.25 mol dm⁻³.

The changes in [Q(aq)] and [R(aq)] are plotted against time until equilibrium is reached. The value of Kc is then calculated.

Which graph and value for Kc are correct?

Oracle Prep · Accepted Answer

The correct answer is C: graph
[Figure 8.3 shows concentration Q decreasing from 0.5 to 0.25 and R increasing from 0 to 0.25] K/mol dm-3
1.

✓ Correct Answer