DP Chemistry (last assessment 2024)

Question 22N.2.hl.TZ0.1f.iii

Date	November 2022	Marks available	[Maximum mark: 2]	Reference code	22N.2.hl.TZ0.1f.iii
Level	hl	Paper	2	Time zone	TZ0
Command term	Calculate	Question number	f.iii	Adapted from	N/A

f.iii.

[Maximum mark: 2]

22N.2.hl.TZ0.1f.iii

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

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

(f.iii)

Calculate the standard enthalpy change, $Δ H^{⦵}$ , of the reaction. Use section 12 of the data booklet.

$Δ H_{f}^{⦵}$ ammonium nitrate = −366 kJ mol⁻¹

$Δ H_{f}^{⦵}$ 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

Slightly fewer students were able to negotiate this calculation, with a number forgetting to double the enthalpy of formation of water, whilst others ignored it all together. In addition some reversed values for the reactants and products.

Syllabus sections

Core

Core » Topic 5: Energetics/thermochemistry » 5.2 Hess’s Law

Core » Topic 5: Energetics/thermochemistry

Question 22N.2.hl.TZ0.1f.iii

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