A-LevelChemistryChemical energetics9701/12 · Oct/Nov 2011 · Q101 Mark

Hess’s Law can be used to calculate the average C–H bond energy in methane. ΔH°at = standard enthalpy change of atomisation ΔH°f = standard enthalpy change of formation ΔH°c = standard enthalpy change of combustion Which data values are needed in order to perform the calculation?

AΔH°f (C), ΔH°f (H), ΔH°f (CH4)

BΔH°at (C), ΔH°at (H2), ΔH°f (CH4)

CΔH°c (C), ΔH°c (H2), ΔH°f (CH4)

DΔH°f (CH4) only, as ΔH°f (C), and ΔH°f (H2), are defined as zero

✓ Correct answer

A: ΔH°f (C), ΔH°f (H), ΔH°f (CH4)

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Topic: Chemical energetics, A-Level Chemistry (syllabus 9701). Multiple choice, 1 mark.
Source: A-Level Chemistry, Oct/Nov 2011 Paper 1 Variant 2, question 10.

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