A-LevelChemistryChemical energetics9701/12 · Oct/Nov 2022 · Q101 Mark

The enthalpy changes for the possible reactions W, X, Y and Z are given. W NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l) ∆H = −56 kJ mol⁻¹ X NaCl(aq) + H2O(l) → NaOH(aq) + HCl(aq) ∆H = +56 kJ mol⁻¹ Y 2HI(g) → H2(g) + I2(g) ∆H° = +11 kJ mol⁻¹ Z H2(g) + I2(g) → 2HI(g) ∆H° = −11 kJ mol⁻¹ Which statement about the activation energies of these reactions is correct?

AX is greater than W; Z is greater than Y.

BX is greater than W; Y is greater than Z.

CW is greater than X; Z is greater than Y.

DW is greater than X; Y is greater than Z.

✓ Correct answer

B: X is greater than W; Y is greater than Z.

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Topic: Chemical energetics, A-Level Chemistry (syllabus 9701). Multiple choice, 1 mark.
Source: A-Level Chemistry, Oct/Nov 2022 Paper 1 Variant 2, question 10.

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