A-LevelChemistryChemical energeticsOct/Nov 2012Paper 1 Q101 Mark
A student calculated the standard enthalpy change of formation of ethane, C2H6, using a method based on standard enthalpy changes of combustion. He used correct values for the standard enthalpy change of combustion of ethane (-1560 kJ mol¯¹) and hydrogen (–286 kJ mol¯¹) but he used an incorrect value for the standard enthalpy change of combustion of carbon. He then performed his calculation correctly. His final answer was –158 kJ mol¯¹. What did he use for the standard enthalpy change of combustion of carbon?
A–1432 kJ mol¯¹
B–860 kJ mol¯¹
C–430 kJ mol¯¹
D–272 kJ mol¯¹
✓ Correct Answer
The correct answer is C: –430 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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