A-LevelChemistryChemical energetics9701/12 · May/June 2023 · Q101 Mark

Nitrogen monoxide is rapidly oxidised to nitrogen dioxide. 2NO(g) + O₂(g) → 2NO₂(g) Nitrogen dioxide can then dimerise to form dinitrogen tetroxide. 2NO₂(g) → N₂O₄(g) ΔH° = –58 kJ mol⁻¹ ΔHᶠNO = +91 kJ mol⁻¹ and ΔHᶠNO₂ = +34 kJ mol⁻¹ What is the value of the standard enthalpy change for the reaction shown? 2NO(g) + O₂(g) → N₂O₄(g)

A+56 kJ mol⁻¹

B–1 kJ mol⁻¹

C–115 kJ mol⁻¹

D–172 kJ mol⁻¹

✓ Correct answer

D: –172 kJ mol⁻¹

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Topic: Chemical energetics, A-Level Chemistry (syllabus 9701). Multiple choice, 1 mark.
Source: A-Level Chemistry, May/June 2023 Paper 1 Variant 2, question 10.

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