A-LevelChemistryChemical energetics9701/12 · Oct/Nov 2015 · Q61 Mark

Hess' law may be used to determine enthalpy changes using average bond energies, as shown in the diagram. [Figure showing U, V, W for reactants, products, isolated gaseous atoms] U is the sum of the average bond energies of the reactants, and V is the sum of the average bond energies of the products. For the reaction shown below, which expression will give a value for W, the enthalpy change of combustion of methane? CH4 + 2O2 → CO2 + 2H2O

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

AU – V

BU + V

C2(U – V)

DV – U

✓ Correct answer

A: U – V

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Topic: Chemical energetics, A-Level Chemistry (syllabus 9701). Multiple choice, 1 mark.
Source: A-Level Chemistry, Oct/Nov 2015 Paper 1 Variant 2, question 6.

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