A-LevelChemistryEquilibriaMay/June 2023Paper 1 Q141 Mark
Hydrogen iodide is added to an evacuated reaction vessel. The vessel is sealed and warmed. A decomposition reaction occurs. Hydrogen and iodine are formed. Some hydrogen iodide remains. When equilibrium is established, the total pressure is 1.20 × 10⁵ Pa. The partial pressure of hydrogen is 4.00 × 10³ Pa. Hydrogen iodide, hydrogen and iodine are all gaseous under the conditions used. What is the value of Kp for the equilibrium at this temperature, assuming the decomposition is the forward reaction?
A1.19 × 10⁻³
B1.28 × 10⁻³
C1.38 × 10⁻³
D1.43 × 10⁻³
✓ Correct Answer
The correct answer is B: 1.28 × 10⁻³
📋 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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