---
title: "The potential energy profile for a three-step reaction mechanism is shown in the graph below.  Based on the profile, which of the following correctly ranks the relative rates of the forward elementary steps from fastest to slowest at a constant temperature, and provides the correct justification?"
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url: "https://nerd-notes.com/ubq/123714/"
date_modified: "2026-09-28T12:02:07+00:00"
---

# The potential energy profile for a three-step reaction mechanism is shown in the graph below.

Based on the profile, which of the following correctly ranks the relative rates of the forward elementary steps from fastest to slowest at a constant temperature, and provides the correct justification?

The potential energy profile for a three-step reaction mechanism is shown in the graph below.

Based on the profile, which of the following correctly ranks the relative rates of the forward elementary steps from fastest to slowest at a constant temperature, and provides the correct justification?

![A potential energy profile graph is displayed on a grayscale coordinate system. The vertical axis is labeled 'Potential Energy (kJ/mol)' with horizontal gridlines and numeric ticks at 0, 10, 20, 30, 40, 50, 60, and 70. The horizontal axis is labeled 'Reaction Progress'. A single solid black curve represents the three-step pathway: it starts at a horizontal plateau at 40 kJ/mol labeled 'Reactants', rises to a first maximum at 70 kJ/mol labeled 'TS_1', descends to a first minimum at 10 kJ/mol labeled 'I_1', rises to a second maximum at 65 kJ/mol labeled 'TS_2', descends to a second minimum at 30 kJ/mol labeled 'I_2', rises to a third maximum at 50 kJ/mol labeled 'TS_3', and finally descends to a horizontal plateau at 0 kJ/mol labeled 'Products'. No other curves, labels, text, or annotations appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1790596927-OZkrJS.jpg)

- **A.** \(\text{Step 3} > \text{Step 1} > \text{Step 2}\), because \(\text{Step 3}\) has the smallest activation energy (\(20 \text{ kJ/mol}\)) and \(\text{Step 2}\) has the largest activation energy (\(55 \text{ kJ/mol}\)).
- **B.** \(\text{Step 3} > \text{Step 2} > \text{Step 1}\), because the activation energy is determined by the absolute peak height, and \(\text{TS}_1\) has the highest potential energy (\(70 \text{ kJ/mol}\)).
- **C.** \(\text{Step 1} > \text{Step 2} > \text{Step 3}\), because the energy difference between the initial reactants and each transition state is greatest for \(\text{Step 1}\).
- **D.** \(\text{Step 2} > \text{Step 1} > \text{Step 3}\), because \(\text{I}_1\) lies in the lowest potential energy well, allowing \(\text{Step 2}\) to proceed most rapidly.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123714/*