AP Chemistry Unit 5.6: Energy Profiles

Practice AP Chemistry Unit 5.6 questions on using activation-energy and particle-energy reasoning to explain how temperature changes reaction rate.

Exam points

Use molecular geometry and intermolecular forces to predict polarity, solubility, and physical properties.
Interpret structural and particle evidence to explain how bonding determines observable behavior.

Covered syllabus points

5.6.A—Represent the activation energy and overall energy change in an elementary reaction using a reaction energy…

[Maximum number: 1]

The half-life $\left(t_{1 / 2}\right)$ of the catalyzed isomerization of cis-2-butene gas to produce trans-2-butene gas, represented above, was measured under various conditions, as shown in the table below.

The half-life of the reaction in trial 4 is less than the half-life in trial 1. Explain why, in terms of activation energy.

The temperature is higher in trial 4, meaning that the $K E_{\text {avg }}$ of the
molecules is greater. Consequently, in this trial a greater fraction of collisions have sufficient energy to overcome the activation energy barrier, thus the rate is greater.

1 point is earned for a correct answer with justification.

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Covered syllabus points

5.6 Reaction Energy Profile question 1