A-LevelChemistryChemical energeticsOct/Nov 2022Paper 1 Q101 Mark
The enthalpy changes for the possible reactions W, X, Y and Z are given. W NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l) ∆H = −56 kJ mol⁻¹ X NaCl(aq) + H2O(l) → NaOH(aq) + HCl(aq) ∆H = +56 kJ mol⁻¹ Y 2HI(g) → H2(g) + I2(g) ∆H° = +11 kJ mol⁻¹ Z H2(g) + I2(g) → 2HI(g) ∆H° = −11 kJ mol⁻¹ Which statement about the activation energies of these reactions is correct?
AX is greater than W; Z is greater than Y.
BX is greater than W; Y is greater than Z.
CW is greater than X; Z is greater than Y.
DW is greater than X; Y is greater than Z.
✓ Correct Answer
The correct answer is B: X is greater than W; Y is greater than Z.
📋 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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