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title: "A rigid, evacuated reaction vessel is filled with \\(\\text{N}_2\\text{(g)}\\) and \\(\\text{H}_2\\text{(g)}\\) and maintained at a constant temperature. The reaction proceeds according to the following equation:\\[\\text{N}_2\\text{(g)} + 3\\,\\text{H}_2\\text{(g)} \\rightleftharpoons 2\\,\\text{NH}_3\\text{(g)}\\]The concentrations of all three species are monitored over time, as shown in the graph below. Based on the graph, which of the following correctly identifies the time when chemical equilibrium is first established and provides the correct justification?"
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url: "https://nerd-notes.com/ubq/120315/"
date_modified: "2026-08-23T04:04:38+00:00"
---

# A rigid, evacuated reaction vessel is filled with \(\text{N}_2\text{(g)}\) and \(\text{H}_2\text{(g)}\) and maintained at a constant temperature. The reaction proceeds according to the following equation:\[\text{N}_2\text{(g)} + 3\,\text{H}_2\text{(g)} \rightleftharpoons 2\,\text{NH}_3\text{(g)}\]The concentrations of all three species are monitored over time, as shown in the graph below. Based on the graph, which of the following correctly identifies the time when chemical equilibrium is first established and provides the correct justification?

A rigid, evacuated reaction vessel is filled with \(\text{N}_2\text{(g)}\) and \(\text{H}_2\text{(g)}\) and maintained at a constant temperature. The reaction proceeds according to the following equation:\[\text{N}_2\text{(g)} + 3\,\text{H}_2\text{(g)} \rightleftharpoons 2\,\text{NH}_3\text{(g)}\]The concentrations of all three species are monitored over time, as shown in the graph below. Based on the graph, which of the following correctly identifies the time when chemical equilibrium is first established and provides the correct justification?

![A line graph with a bare vertical axis labeled Concentration (\(\text{mol/L}\)) with numeric tick marks at 0.0, 0.5, 1.0, 1.5, 2.0, and 2.5, and a horizontal axis labeled Time (\(\text{s}\)) with marked points 0, t_0, t_1, and t_2 in chronological order. Three distinct grayscale curves are plotted: 1. A solid black curve labeled [\(\text{H}_2\)] begins at (0, 2.0), decreases downward, intersects the dotted curve at time t_0, and levels off horizontally at 0.8 mol/L starting at time t_1, remaining flat through t_2. 2. A dashed black curve labeled [\(\text{N}_2\)] begins at (0, 1.0), decreases downward gradually, and levels off horizontally at 0.6 mol/L starting at time t_1, remaining flat through t_2. 3. A dotted black curve labeled [\(\text{NH}_3\)] begins at (0, 0.0), increases upward, intersects the solid curve at time t_0, and levels off horizontally at 0.8 mol/L starting at time t_1, remaining flat through t_2. No other curves, points, text, or annotations appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1787457878-IN6W5b.jpg)

- **A.** At time \(t_0\), because the concentration of the product \(\text{NH}_3\) becomes equal to the concentration of the reactant \(\text{H}_2\).
- **B.** At time \(t_1\), because the concentrations of all species become constant as the rates of the forward and reverse reactions become equal.
- **C.** At time \(t_1\), because both the forward and reverse reactions stop occurring once the concentration plateaus are reached.
- **D.** At time \(t_2\), because the system requires additional time after leveling off to achieve the maximum yield of \(\text{NH}_3\).

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/120315/*