---
title: "A potential energy profile for the uncatalyzed elementary gas-phase reaction \\(\\text{A}_2\\text{(g)} + \\text{B}_2\\text{(g)} \\rightleftharpoons 2\\text{AB(g)}\\) is shown in the diagram.  When a catalyst is added to the reaction vessel, it provides an alternate pathway with an activation energy of \\(50\\text{ kJ/mol}\\) for the forward reaction. Which of the following predicts the activation energy of the reverse reaction, \\(E_{a,\\text{rev}}\\), for the catalyzed pathway and provides the correct justification?"
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url: "https://nerd-notes.com/ubq/121439/"
date_modified: "2026-08-23T05:02:22+00:00"
---

# A potential energy profile for the uncatalyzed elementary gas-phase reaction \(\text{A}_2\text{(g)} + \text{B}_2\text{(g)} \rightleftharpoons 2\text{AB(g)}\) is shown in the diagram.

When a catalyst is added to the reaction vessel, it provides an alternate pathway with an activation energy of \(50\text{ kJ/mol}\) for the forward reaction. Which of the following predicts the activation energy of the reverse reaction, \(E_{a,\text{rev}}\), for the catalyzed pathway and provides the correct justification?

A potential energy profile for the uncatalyzed elementary gas-phase reaction \(\text{A}_2\text{(g)} + \text{B}_2\text{(g)} \rightleftharpoons 2\text{AB(g)}\) is shown in the diagram.

When a catalyst is added to the reaction vessel, it provides an alternate pathway with an activation energy of \(50\text{ kJ/mol}\) for the forward reaction. Which of the following predicts the activation energy of the reverse reaction, \(E_{a,\text{rev}}\), for the catalyzed pathway and provides the correct justification?

![A two-dimensional potential energy diagram with a horizontal reaction coordinate axis and a vertical potential energy axis labeled 'Potential Energy (kJ/mol)'. The vertical axis has four labeled tick marks at 0, 20, 50, and 130. A single solid curve represents the uncatalyzed reaction path. The curve begins on the left at a horizontal plateau at 50 kJ/mol representing the reactants labeled A2(g) + B2(g). The curve rises smoothly to a single rounded maximum at 130 kJ/mol representing the transition state. The curve then descends smoothly to a horizontal plateau on the right at 20 kJ/mol representing the products labeled 2 AB(g). Horizontal dashed reference lines extend from 130, 50, and 20 kJ/mol across the profile to the vertical axis. No other curves, shaded regions, labels, or annotations appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1787461342-22ZPWd.jpg)

- **A.** \(50\text{ kJ/mol}\), because a catalyst reduces the activation energy of both the forward and reverse reactions to the same numerical value.
- **B.** \(80\text{ kJ/mol}\), because the catalyst lowers the transition state energy for both directions while the overall enthalpy of reaction, \(\Delta H^\circ\), remains \(-30\text{ kJ/mol}\).
- **C.** \(110\text{ kJ/mol}\), because a catalyst lowers the activation energy of the forward reaction only and does not alter the reverse activation energy barrier.
- **D.** \(140\text{ kJ/mol}\), because the catalyst stabilizes the reactants relative to the products, making the reverse reaction more endothermic by \(30\text{ kJ/mol}\).

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/121439/*