DP Chemistry (last assessment 2024)

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Question 22N.2.sl.TZ0.f.iii

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Date November 2022 Marks available [Maximum mark: 2] Reference code 22N.2.sl.TZ0.f.iii
Level sl Paper 2 Time zone TZ0
Command term Calculate Question number f.iii Adapted from N/A
f.iii.
[Maximum mark: 2]
22N.2.sl.TZ0.f.iii

Ammonium nitrate, NH4NO3, is used as a high nitrogen fertilizer.

Solid ammonium nitrate can decompose to gaseous dinitrogen monoxide and liquid water.

Calculate the standard enthalpy change, ΔH⦵, of the reaction. Use section 12 of the data booklet.

ΔHf⦵ ammonium nitrate = −366 kJ mol−1

ΔHf⦵ dinitrogen monoxide = 82 kJ mol−1

[2]

Markscheme

2 x –285.8 «kJ mol−1» ✔


«1 mol (82 kJ mol−1) + 2 mol (– 285.8 kJ mol−1) – 1 mol (–366 kJ mol−1) =» –124 «kJ» ✔

 

Award [2] for correct final answer.

Examiners report

Less than half of the candidates were able to calculate the standard enthalpy change correctly. Errors included not including DHf of water, not multiplying DHf of water by two, subtracting incorrectly (reactants − products), and arithmetic errors. This question also had a high discrimination index.

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