Question 22M.2.hl.TZ1.a(iii)
| Date | May 2022 | Marks available | [Maximum mark: 3] | Reference code | 22M.2.hl.TZ1.a(iii) |
| Level | hl | Paper | 2 | Time zone | TZ1 |
| Command term | Explain | Question number | a(iii) | Adapted from | N/A |
Ammonia is produced by the Haber–Bosch process which involves the equilibrium:
N2 (g) + 3 H2 (g) 2 NH3 (g)
The percentage of ammonia at equilibrium under various conditions is shown:
[The Haber Bosch Process [graph] Available at: https://commons.wikimedia.org/wiki/File:Ammonia_yield.png
[Accessed: 16/07/2022].]
With reference to the reaction quotient, Q, explain why the percentage yield increases as the pressure is increased at constant temperature.
[3]
increasing pressure increases «all» concentrations
OR
increasing pressure decreases volume ✔
Q becomes less than Kc
OR
affects the lower line/denominator of Q expression more than upper line/numerator ✔
«for Q to once again equal Kc,» ratio of products to reactants increases
OR
«for Q to once again equal Kc,» equilibrium shifts to right/products ✔
Award [2 max] for answers that do not refer to Q.
Mediocre performance; very few identified the effect of increasing pressure on all concentrations. Consequently, Q becomes less than Kc (it affects the denominator of Q expression more than the numerator) was not addressed. Question was often answered with respect to kinetics, namely greater frequency of collisions and speed of reaction rather than from equilibrium perspective based on effect of increase in pressure on concentrations.
