A-LevelChemistryChemical energeticsMay/June 2011Paper 1 Q91 Mark
In the conversion of compound X into compound Z, it was found that the reaction proceeded by way of compound Y, which could be isolated. The following steps were involved. X → Y ; ΔH, positive Y → Z ; ∆H, negative Which reaction profile fits these data? [Figure 9.1]
A[Diagram A: Reaction profile with X as reactant, Y as intermediate (higher energy than X), Z as product (lower energy than Y but higher than X), with activation barriers shown]
B[Diagram B: Reaction profile with X as reactant, Y as intermediate (higher energy than X), Z as product (lower energy than Y but lower than X), with activation barriers shown]
C[Diagram C: Reaction profile with X as reactant, Y as intermediate (lower energy than X), Z as product (lower energy than Y), with activation barriers shown]
D[Diagram D: Reaction profile with X as reactant, Y as intermediate (higher energy than X), Z as product (lower energy than X but higher than Y), with activation barriers shown]
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The correct answer is A. This question tests the candidate's understanding of chemical energetics within the Chemistrysyllabus. The examiner's mark scheme requires...
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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...
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