---
title: "A student investigates the decomposition of ethanol vapor catalyzed by a heated platinum surface, represented by the following equation.  \\[ \\text{C}_2\\text{H}_5\\text{OH}(g) \\xrightarrow{\\text{Pt}(s)} \\text{CH}_3\\text{CHO}(g) + \\text{H}_2(g) \\]  The student determines that at high initial partial pressures of \\(\\text{C}_2\\text{H}_5\\text{OH}(g)\\), the rate of product formation is constant over time and does not change when additional \\(\\text{C}_2\\text{H}_5\\text{OH}(g)\\) is introduced into the reaction vessel. Which of the following correctly identifies the reaction order with respect to \\(\\text{C}_2\\text{H}_5\\text{OH}\\) under these conditions and provides the best explanation?"
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url: "https://nerd-notes.com/ubq/123648/"
date_modified: "2026-09-28T12:01:53+00:00"
---

# A student investigates the decomposition of ethanol vapor catalyzed by a heated platinum surface, represented by the following equation.

\[ \text{C}_2\text{H}_5\text{OH}(g) \xrightarrow{\text{Pt}(s)} \text{CH}_3\text{CHO}(g) + \text{H}_2(g) \]

The student determines that at high initial partial pressures of \(\text{C}_2\text{H}_5\text{OH}(g)\), the rate of product formation is constant over time and does not change when additional \(\text{C}_2\text{H}_5\text{OH}(g)\) is introduced into the reaction vessel. Which of the following correctly identifies the reaction order with respect to \(\text{C}_2\text{H}_5\text{OH}\) under these conditions and provides the best explanation?

A student investigates the decomposition of ethanol vapor catalyzed by a heated platinum surface, represented by the following equation.

\[ \text{C}_2\text{H}_5\text{OH}(g) \xrightarrow{\text{Pt}(s)} \text{CH}_3\text{CHO}(g) + \text{H}_2(g) \]

The student determines that at high initial partial pressures of \(\text{C}_2\text{H}_5\text{OH}(g)\), the rate of product formation is constant over time and does not change when additional \(\text{C}_2\text{H}_5\text{OH}(g)\) is introduced into the reaction vessel. Which of the following correctly identifies the reaction order with respect to \(\text{C}_2\text{H}_5\text{OH}\) under these conditions and provides the best explanation?

- **A.** The reaction is zero-order with respect to \(\text{C}_2\text{H}_5\text{OH}\) because the active catalytic sites on the platinum surface are saturated, making the rate of reaction independent of the gas-phase reactant concentration.
- **B.** The reaction is zero-order with respect to \(\text{C}_2\text{H}_5\text{OH}\) because the activation energy of the catalytic decomposition pathway increases as the concentration of \(\text{C}_2\text{H}_5\text{OH}(g)\) increases.
- **C.** The reaction is first-order with respect to \(\text{C}_2\text{H}_5\text{OH}\) because the frequency of collisions between \(\text{C}_2\text{H}_5\text{OH}\) molecules and the platinum surface increases as partial pressure increases.
- **D.** The reaction is first-order with respect to \(\text{C}_2\text{H}_5\text{OH}\) because the rate constant \(k\) increases proportionally with the partial pressure of \(\text{C}_2\text{H}_5\text{OH}(g)\) at constant temperature.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123648/*