DP Chemistry (last assessment 2024)

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Question 22M.2.hl.TZ1.c(ii)

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Date May 2022 Marks available [Maximum mark: 2] Reference code 22M.2.hl.TZ1.c(ii)
Level hl Paper 2 Time zone TZ1
Command term Calculate Question number c(ii) Adapted from N/A
c(ii).
[Maximum mark: 2]
22M.2.hl.TZ1.c(ii)

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].]

The standard free energy change, ΔG⦵, for the Haber–Bosch process is –33.0 kJ at 298 K.

Calculate the value of the equilibrium constant, K, at 298 K. Use sections 1 and 2 of the data booklet.

[2]

Markscheme

ln K=⟨⟨∆GR.T=⟩⟩ --330008.31x298 /«+»13.3 ✔

K = 6.13×105 ✔

 

Award [2] for correct final answer.

Accept answers in the range 4.4×105 to 6.2×105 (arises from rounding of ln K).

Examiners report

Good performance; for lnK calculation in the equation ΔG = RTlnK, ΔG unit had to be converted from kJ to J. This led to an error of 1000 in the value of lnK for some.

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