---
title: "A rigid 1.0 L vessel contains an equilibrium mixture of \\(\\text{X(g)}\\) and \\(\\text{Y(g)}\\) according to the following balanced equation:  \\(\\text{X(g)} \\rightleftharpoons 2\\text{Y(g)}\\)  At time \\(t_1\\), additional \\(\\text{Y(g)}\\) is rapidly injected into the vessel at constant temperature. The concentration versus time graph for the system is shown below. Based on the graph, which statement correctly describes and explains the behavior of the system as it approaches a new equilibrium between \\(t_1\\) and \\(t_2\\)?"
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url: "https://nerd-notes.com/ubq/119394/"
date_modified: "2026-08-19T12:40:06+00:00"
---

# A rigid 1.0 L vessel contains an equilibrium mixture of \(\text{X(g)}\) and \(\text{Y(g)}\) according to the following balanced equation:

\(\text{X(g)} \rightleftharpoons 2\text{Y(g)}\)

At time \(t_1\), additional \(\text{Y(g)}\) is rapidly injected into the vessel at constant temperature. The concentration versus time graph for the system is shown below. Based on the graph, which statement correctly describes and explains the behavior of the system as it approaches a new equilibrium between \(t_1\) and \(t_2\)?

A rigid 1.0 L vessel contains an equilibrium mixture of \(\text{X(g)}\) and \(\text{Y(g)}\) according to the following balanced equation:

\(\text{X(g)} \rightleftharpoons 2\text{Y(g)}\)

At time \(t_1\), additional \(\text{Y(g)}\) is rapidly injected into the vessel at constant temperature. The concentration versus time graph for the system is shown below. Based on the graph, which statement correctly describes and explains the behavior of the system as it approaches a new equilibrium between \(t_1\) and \(t_2\)?

![A concentration versus time line graph with horizontal axis labeled 'Time' with marked points t_1 and t_2, and vertical axis labeled 'Concentration (M)' ranging from 0.00 to 0.90 M with gridlines every 0.10 M. Two curves are drawn in black ink. Curve 1 (solid black line) represents [X]. Curve 2 (dashed black line) represents [Y]. From time 0 to t_1, both curves are flat horizontal lines: solid line [X] is constant at 0.40 M, dashed line [Y] is constant at 0.40 M. At time t_1, the solid line [X] remains at 0.40 M without a vertical step. At time t_1, the dashed line [Y] shows a vertical step upward from 0.40 M to 0.80 M. Between t_1 and t_2, the dashed line [Y] curves smoothly downward from 0.80 M to 0.60 M, where it levels off horizontally at t_2. Between t_1 and t_2, the solid line [X] curves smoothly upward from 0.40 M to 0.50 M, where it levels off horizontally at t_2. From t_2 onward, both curves remain horizontal.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1787143205-rIRXJv.jpg)

- **A.** The system shifts toward products because the addition of \(\text{Y(g)}\) increases the rate of the forward reaction, causing \([\text{X}]\) to decrease.
- **B.** The system shifts toward reactants because \(Q > K_c\), with \([\text{X}]\) increasing by twice the amount that \([\text{Y}]\) decreases.
- **C.** The system shifts toward reactants because \(Q > K_c\), with \([\text{Y}]\) decreasing by twice the amount that \([\text{X}]\) increases.
- **D.** The system shifts toward reactants because adding \(\text{Y(g)}\) decreases the value of \(K_c\), forcing the system to favor the reverse reaction.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119394/*