---
title: "The hydrogenation of ethene to form ethane in the presence of a solid platinum catalyst is represented by the following chemical equation:  \\[ \\text{C}_2	ext{H}_4\\text{(g)} + \\text{H}_2\\text{(g)} \\xrightarrow{\\text{Pt(s)}} \\text{C}_2\\text{H}_6\\text{(g)} \\]  A proposed particulate-level mechanism for this heterogeneous catalytic process is shown in the four sequential stages below.  Based on the representations, which of the following best explains how the interaction between the reactant molecules and the \\(\\text{Pt}\\) catalyst surface lowers the activation energy (\\(E_a\\)) of the reaction compared to the uncatalyzed gas-phase reaction?"
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url: "https://nerd-notes.com/ubq/123718/"
date_modified: "2026-09-28T12:02:08+00:00"
---

# The hydrogenation of ethene to form ethane in the presence of a solid platinum catalyst is represented by the following chemical equation:

\[ \text{C}_2	ext{H}_4\text{(g)} + \text{H}_2\text{(g)} \xrightarrow{\text{Pt(s)}} \text{C}_2\text{H}_6\text{(g)} \]

A proposed particulate-level mechanism for this heterogeneous catalytic process is shown in the four sequential stages below.

Based on the representations, which of the following best explains how the interaction between the reactant molecules and the \(\text{Pt}\) catalyst surface lowers the activation energy (\(E_a\)) of the reaction compared to the uncatalyzed gas-phase reaction?

The hydrogenation of ethene to form ethane in the presence of a solid platinum catalyst is represented by the following chemical equation:

\[ \text{C}_2	ext{H}_4\text{(g)} + \text{H}_2\text{(g)} \xrightarrow{\text{Pt(s)}} \text{C}_2\text{H}_6\text{(g)} \]

A proposed particulate-level mechanism for this heterogeneous catalytic process is shown in the four sequential stages below.

Based on the representations, which of the following best explains how the interaction between the reactant molecules and the \(\text{Pt}\) catalyst surface lowers the activation energy (\(E_a\)) of the reaction compared to the uncatalyzed gas-phase reaction?

![A diagram with four horizontal panels labeled Stage 1, Stage 2, Stage 3, and Stage 4. A legend maps: small open circle = H atom, medium filled black circle = C atom, large gray hatched circle = Pt atom. In each panel, the bottom contains a catalyst slab of exactly 12 Pt atoms in two rows of 6. Stage 1 shows one separate H2 molecule (two bonded open circles) and one C2H4 molecule (two bonded black circles, each with two open circles) in the space above the slab. Stage 2 shows two dissociated open circles bonded to adjacent surface Pt atoms, and the two black circles of C2H4 bonded to adjacent surface Pt atoms. Stage 3 shows a C2H5 group bonded to one surface Pt atom and one open circle bonded to an adjacent Pt atom. Stage 4 shows one intact C2H6 molecule above the bare Pt surface. No other particles, labels, text, or annotations appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1790596928-QKF0uW.jpg)

- **A.** The platinum surface increases the average kinetic energy of the reactant molecules, thereby shifting the Maxwell-Boltzmann distribution toward higher velocities and increasing the collision frequency.
- **B.** The platinum surface adsorbs the reactants and facilitates the breaking of the \(\text{H}-\text{H}\) bond and weakening of the \(\text{C}=\text{C}\) \(\pi\) bond, providing an alternate reaction pathway with a lower activation energy.
- **C.** The platinum surface alters the thermodynamic favorability of the overall reaction by lowering the potential energy of the gaseous \(\text{C}_2\text{H}_6\) product molecules, making \(\Delta H^\circ\) significantly more negative.
- **D.** The platinum surface functions as a sacrificial electron donor that permanently reduces the carbon atoms to carbanions, eliminating the activation energy barrier required to form \(\text{C}-\text{H}\) bonds.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123718/*