A-LevelChemistryEquilibriaMay/June 2025Paper 1 Q41 Mark
The reaction between sulfur dioxide and oxygen has the equation shown. 2SO2(g) + O2(g) ⇌ 2SO3(g) ΔH = –197 kJ mol⁻¹ 1.0 mol of SO2 and 1.0 mol of O2 are placed in a closed container and heated to a constant temperature. At this temperature, 0.8 mol of SO3 are present in the equilibrium mixture. Which statement is correct?
AThe equilibrium partial pressure of SO2 is greater than the equilibrium partial pressure of O2.
BKp has units of mol dm⁻³.
CAt a lower temperature, the equilibrium amount of SO3 is lower than 0.8 mol.
DThe mole fraction of SO3 is less than 0.8.
✓ Correct Answer
The correct answer is D: The mole fraction of SO3 is less than 0.8.
📋 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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