A-LevelChemistryChemical energetics9701/12 · Oct/Nov 2011 · Q171 Mark

The standard enthalpy changes of formation of HCl and HI are –92 kJ mol⁻¹ and +26 kJ mol⁻¹ respectively. Which statement is most important in explaining this difference?

AChlorine is more electronegative than iodine.

BThe activation energy for the H2 + Cl2 reaction is much less than that for the H2 + I2 reaction.

CThe bond energy of HI is smaller than the bond energy of HCl.

DThe bond energy of I2 is smaller than the bond energy of Cl2.

✓ Correct answer

C: The bond energy of HI is smaller than the bond energy of HCl.

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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 17.

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