---
title: "The reversible reaction between diatomic gases \\(\\text{X}_2(g)\\) and \\(\\text{Y}_2(g)\\) is represented by the equation below.  \\[\\text{X}_2(g) + \\text{Y}_2(g) \\rightleftharpoons 2\\,\\text{XY}(g) \\quad K_c = 4.0\\]  A mixture of \\(\\text{X}_2(g)\\), \\(\\text{Y}_2(g)\\), and \\(\\text{XY}(g)\\) is contained in a rigid vessel of fixed volume at constant temperature, as represented in the particulate diagram. Which of the following statements best explains whether the system is at equilibrium?"
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url: "https://nerd-notes.com/ubq/119811/"
date_modified: "2026-08-21T08:12:27+00:00"
---

# The reversible reaction between diatomic gases \(\text{X}_2(g)\) and \(\text{Y}_2(g)\) is represented by the equation below.

\[\text{X}_2(g) + \text{Y}_2(g) \rightleftharpoons 2\,\text{XY}(g) \quad K_c = 4.0\]

A mixture of \(\text{X}_2(g)\), \(\text{Y}_2(g)\), and \(\text{XY}(g)\) is contained in a rigid vessel of fixed volume at constant temperature, as represented in the particulate diagram. Which of the following statements best explains whether the system is at equilibrium?

The reversible reaction between diatomic gases \(\text{X}_2(g)\) and \(\text{Y}_2(g)\) is represented by the equation below.

\[\text{X}_2(g) + \text{Y}_2(g) \rightleftharpoons 2\,\text{XY}(g) \quad K_c = 4.0\]

A mixture of \(\text{X}_2(g)\), \(\text{Y}_2(g)\), and \(\text{XY}(g)\) is contained in a rigid vessel of fixed volume at constant temperature, as represented in the particulate diagram. Which of the following statements best explains whether the system is at equilibrium?

![A single square container with a solid black border. A legend at the top defines: a pair of touching open white circles represents an \(\text{X}_2\) molecule, a pair of touching solid black circles represents a \(\text{Y}_2\) molecule, and a pair consisting of one open white circle touching one solid black circle represents an \(\text{XY}\) molecule. Inside the container, there are exactly 2 \(\text{X}_2\) molecules, exactly 2 \(\text{Y}_2\) molecules, and exactly 4 \(\text{XY}\) molecules, distributed uniformly throughout the space. Individual particles are unlabeled. No other particles, labels, text, or annotations appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1787299947-1qxpt6.jpg)

- **A.** The system is not at equilibrium and will shift toward products because \(Q_c = 1.0\), which is less than \(K_c\).
- **B.** The system is not at equilibrium and will shift toward reactants because \(Q_c = 8.0\), which is greater than \(K_c\).
- **C.** The system is at equilibrium because \(Q_c = 4.0\), which is equal to \(K_c\).
- **D.** The system is at equilibrium because the total number of product molecules is equal to the total number of reactant molecules.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119811/*