A-LevelChemistryEquilibria9701/12 · Oct/Nov 2022 · Q81 Mark
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 uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Agraph
[Figure 8.1 shows concentration Q decreasing from 0.5 to 0.25 and R increasing from 0 to 0.5] K/mol dm-3
1
Bgraph
[Figure 8.2 shows concentration Q decreasing from 0.5 to 0.25 and R increasing from 0 to 0.5] K/mol dm-3
0.25
Cgraph
[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
Dgraph
[Figure 8.4 shows concentration Q decreasing from 0.5 to 0.25 and R increasing from 0 to 0.25] K/mol dm-3
2
✓ Correct answer
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
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