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CAIE A-Level Chemistry 5.1.6 Exact and Average Bond Energies

Practise distinguishing a bond energy measured for one gaseous molecule from an average value across different compounds.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • treat a bond energy for a specified diatomic gaseous molecule as an exact value for that species
  • recognize that a named bond such as C–H has different energies in different molecular environments
  • use an average bond energy for general calculations and explain why the resulting ΔH may differ from experiment

5.1.6—Some bond energies are exact and some bond question 1

[Maximum number: 1]

The table shows bond energies for some diatomic molecules. Deuterium, D, is an isotope of hydrogen.

Table for Question 5.1.6—Some bond energies are exact and some bond question 1 — CAIE A-Level Chemistry AS

Which statements are correct?

1 Diatomic molecules have exact values for their bond energies, which are always positive.

2 The trend in Group 7 bond energies can be explained by the variation in instantaneous dipole-induced dipole (id-id) forces.

3 A value for the enthalpy change for the reaction between deuterium and chlorine can be calculated using these data alone.

A

1 only

B

1 and 2 only

C

1 and 3 only

D

2 and 3 only

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