DP Chemistry (last assessment 2024)

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Question 19M.2.hl.TZ1.6f(iii)

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Date May 2019 Marks available [Maximum mark: 2] Reference code 19M.2.hl.TZ1.6f(iii)
Level hl Paper 2 Time zone TZ1
Command term Calculate Question number f(iii) Adapted from N/A
f(iii).
[Maximum mark: 2]
19M.2.hl.TZ1.6f(iii)

This question is about iron.

(f(iii))

Calculate a value for the equilibrium constant, Kc, at 298 K, giving your answer to two significant figures. Use your answer to (f)(ii) and section 1 of the data booklet. 

(If you did not obtain an answer to (f)(ii), use −140 kJ mol−1, but this is not the correct value.)

[2]

Markscheme

«lnKc = − Δ G θ R T = − − 152 × 10 3  Jmo l − 1 8.31 J K − 1 mo l − 1 × 298 K =» 61.38    [✔]

K = 4.5 × 1026    [✔]

 

Note: Accept answers in range 2.0 × 1026 to 5.5 × 1026.

Do not award M2 if answer not given to two significant figures.

If −140 kJmol−1 used, answer is 3.6 × 1024.

Examiners report

This question was left blank by quite a few candidates. Common errors included not using correct units, or more often, calculation error in converting ln Kc into Kc value.

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