Agreement, Complement, and Disagreement to “Why Are Some Reactions Slower at Higher Temperatures?”

Abstract

In the article “Why Are Some Reactions Slower at Higher Temperatures?” published in this Journal, Revell and Williamson explained, from the enthalpic and entropic aspects, why an A + B → P reaction may proceed more slowly at higher temperatures via an A + B ↔ C → P mechanism using the pre-equilibrium approximation. Their explanation is convincing but may be too abstract for undergraduate physical chemistry students to understand fully. In this communication, a numerical implementation and graphical demonstrations of their explanation are provided for students to use to “see” for themselves a negative activation energy. Although Revell and Williamson perfectly explained the negative temperature dependence of the A + B ↔ C → P reaction rate, great caution must be exercised when their explanation is applied to interstellar chemistry where the pre-equilibrium approximation may be invalid and statistical thermodynamics functions may be ill-defined.