AP Chemistry Unit 6.7: Bond Enthalpy

Practice AP Chemistry Unit 6.7 questions on estimating reaction enthalpy by comparing average bond energies for bonds broken and bonds formed.

Exam points

Use equilibrium, acid–base, and solubility models to predict pH, species, precipitation, and reaction direction.
Calculate or interpret Ka, Kb, Ksp, concentrations, and titration data from balanced equations and experiments.

Covered syllabus points

6.7.A—Calculate the enthalpy change of a reaction based on the average bond energies of bonds broken and formed in the…

[Maximum number: 1]

Answer the following questions relating to the chemistry of the halogens.

Calculate the bond energy of the Br-Cl bond, in kJ/mol, using $\Delta H^{\circ}$ for the reaction $\left(1.6 \mathrm{~kJ} / \mathrm{mol}_{\text {rxn }}\right)$ and the information in the following table.

Table for Question 6.7 Bond Enthalpies question 1 — AP Chemistry

\begin{aligned} & \Delta H^{\circ}=\sum(\text { bond energies })_{\text {broken }}-\sum(\text { bond energies })_{\text {formed }} \\ & 1.6 \mathrm{~kJ} / \mathrm{mol}=2(\mathrm{Br}-\mathrm{Cl} \text { bond energy })-(193 \mathrm{~kJ} / \mathrm{mol}+243 \mathrm{~kJ} / \mathrm{mol}) \\ & (436+1.6) \mathrm{kJ} / \mathrm{mol}=2(\mathrm{Br}-\mathrm{Cl} \text { bond energy }) \\ & \mathrm{Br}-\mathrm{Cl} \text { bond energy }=219 \mathrm{~kJ} / \mathrm{mol} \end{aligned}

1 point is earned for a correct calculation of the Br-Cl bond energy.

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Covered syllabus points

6.7 Bond Enthalpies question 1