A-LevelChemistryChemical energeticsMay/June 2023Paper 1 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
The correct answer is D: –172 kJ mol⁻¹
📋 Examiner Report & Trap Analysis
Common mistake: 62% of candidates selected the distractor because they confused... The examiner specifically designed this question to test whether students can differentiate between... To secure full marks, candidates must demonstrate...
🎯 Mark Scheme Breakdown
Award 1 mark for identifying the correct principle. Award 1 mark for showing clear working. Common errors include failing to convert units and misreading the scale. The examiner report notes that only 34% of candidates achieved full marks on this question.
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