DP Chemistry (last assessment 2024)

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Question 21N.2.hl.TZ0.3c(iv)

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Date November 2021 Marks available [Maximum mark: 2] Reference code 21N.2.hl.TZ0.3c(iv)
Level hl Paper 2 Time zone TZ0
Command term Determine Question number c(iv) Adapted from N/A
c(iv).
[Maximum mark: 2]
21N.2.hl.TZ0.3c(iv)

White phosphorus is an allotrope of phosphorus and exists as P4.

An equilibrium exists between PCl3 and PCl5.

PCl3 (g) + Cl2 (g) ⇌ PCl5 (g)

(c(iv))

Determine the equilibrium constant, K, for this reaction at 25 °C, referring to section 1 of the data booklet.

If you did not obtain an answer in (c)(iii), use ΔG = –43.5 kJ mol−1, but this is not the correct answer.

[2]

Markscheme

«ΔG = –41.8 kJ mol–1 = -8.31 J mol-1 K-11000 × 298 K × lnK»
OR
«ΔG = –41800 J mol–1 = –8.31 J mol–1 K–1 × 298 K × lnK»

«lnK = =» 16.9 ✔

«K = e16.9 =» 2.19 × 107 ✔

 

Award [2] for correct final answer.

Accept range of 1.80 × 106–2.60 × 107.

If –43.5 is used then 4.25 × 107.

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