---
title: "A closed system at constant temperature and pressure contains a gaseous mixture undergoing the reversible reaction represented below.  \\[ \\text{X(g)} \\rightleftharpoons \\text{Y(g)} \\]  The graph shows the total Gibbs free energy, \\(G\\), of the system as a function of the reaction progress from pure \\(\\text{X(g)}\\) to pure \\(\\text{Y(g)}\\). Point \\(E\\) marks the minimum of the curve.  Which of the following statements correctly interprets the thermodynamic state of the system at the indicated point?"
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url: "https://nerd-notes.com/ubq/123943/"
date_modified: "2026-09-28T12:32:23+00:00"
---

# A closed system at constant temperature and pressure contains a gaseous mixture undergoing the reversible reaction represented below.

\[ \text{X(g)} \rightleftharpoons \text{Y(g)} \]

The graph shows the total Gibbs free energy, \(G\), of the system as a function of the reaction progress from pure \(\text{X(g)}\) to pure \(\text{Y(g)}\). Point \(E\) marks the minimum of the curve.

Which of the following statements correctly interprets the thermodynamic state of the system at the indicated point?

A closed system at constant temperature and pressure contains a gaseous mixture undergoing the reversible reaction represented below.

\[ \text{X(g)} \rightleftharpoons \text{Y(g)} \]

The graph shows the total Gibbs free energy, \(G\), of the system as a function of the reaction progress from pure \(\text{X(g)}\) to pure \(\text{Y(g)}\). Point \(E\) marks the minimum of the curve.

Which of the following statements correctly interprets the thermodynamic state of the system at the indicated point?

![A line graph plotted on bare grayscale axes without gridlines. The horizontal axis is labeled 'Reaction Progress' with a left tick labeled 'Pure \(\text{X(g)}\)' and a right tick labeled 'Pure \(\text{Y(g)}\)'. The vertical axis is labeled 'Total Gibbs Free Energy, \(G\)'. A single solid black curve starts at the left vertical axis at an initial height labeled Point \(P\), curves downward with a decreasing negative slope to a distinct minimum at Point \(E\) located at approximately \(75\%\) along the horizontal axis, and then rises with an increasing positive slope to the right vertical axis at Point \(Z\). The height of Point \(Z\) is distinctly lower than Point \(P\). A solid dot on the downward slope is labeled Point \(W\). A solid dot at the trough is labeled Point \(E\). A solid dot on the upward slope is labeled Point \(Y\). A vertical dashed dimension line between the height of Point \(P\) and Point \(Z\) is labeled '\(\Delta G^\circ\)'. No other particles, labels, text, or annotations appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1790598743-DHRBUS.jpg)

- **A.** At Point \(W\), the forward reaction is spontaneous because \(Q > K\), driven by \(\Delta G^\circ < 0\).
- **B.** At Point \(E\), \(\Delta G^\circ = 0\) because the system has reached dynamic equilibrium with equal concentrations of reactants and products.
- **C.** At Point \(E\), \(\Delta G = 0\) and \(Q = K\), which occurs at an intermediate composition even though \(\Delta G^\circ < 0\).
- **D.** At Point \(Y\), \(\Delta G < 0\) because the reaction continues spontaneously toward pure \(\text{Y(g)}\) to minimize \(\Delta G^\circ\).

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123943/*