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title: "A rigid vessel contains an equilibrium mixture of \\(\\text{N}_2\\text{(g)}\\), \\(\\text{O}_2\\text{(g)}\\), and \\(\\text{NO(g)}\\) at an initial temperature of \\(800\\text{ K}\\), according to the endothermic reaction represented below.  \\[ \\text{N}_2\\text{(g)} + \\text{O}_2\\text{(g)} \\rightleftharpoons 2\\,\\text{NO(g)} \\quad \\Delta H^\\circ = +180\\text{ kJ/mol}_{\\text{rxn}} \\]  The temperature of the container is rapidly lowered to \\(600\\text{ K}\\) while the volume remains constant. Which of the following statements best describes the relationship between the reaction quotient, \\(Q_p\\), and the new equilibrium constant, \\(K_p\\), immediately after the temperature change, and correctly predicts the direction the system will shift to re-establish equilibrium?"
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url: "https://nerd-notes.com/ubq/120290/"
date_modified: "2026-08-23T04:04:18+00:00"
---

# A rigid vessel contains an equilibrium mixture of \(\text{N}_2\text{(g)}\), \(\text{O}_2\text{(g)}\), and \(\text{NO(g)}\) at an initial temperature of \(800\text{ K}\), according to the endothermic reaction represented below.

\[ \text{N}_2\text{(g)} + \text{O}_2\text{(g)} \rightleftharpoons 2\,\text{NO(g)} \quad \Delta H^\circ = +180\text{ kJ/mol}_{\text{rxn}} \]

The temperature of the container is rapidly lowered to \(600\text{ K}\) while the volume remains constant. Which of the following statements best describes the relationship between the reaction quotient, \(Q_p\), and the new equilibrium constant, \(K_p\), immediately after the temperature change, and correctly predicts the direction the system will shift to re-establish equilibrium?

A rigid vessel contains an equilibrium mixture of \(\text{N}_2\text{(g)}\), \(\text{O}_2\text{(g)}\), and \(\text{NO(g)}\) at an initial temperature of \(800\text{ K}\), according to the endothermic reaction represented below.

\[ \text{N}_2\text{(g)} + \text{O}_2\text{(g)} \rightleftharpoons 2\,\text{NO(g)} \quad \Delta H^\circ = +180\text{ kJ/mol}_{\text{rxn}} \]

The temperature of the container is rapidly lowered to \(600\text{ K}\) while the volume remains constant. Which of the following statements best describes the relationship between the reaction quotient, \(Q_p\), and the new equilibrium constant, \(K_p\), immediately after the temperature change, and correctly predicts the direction the system will shift to re-establish equilibrium?

- **A.** \(Q_p < K_p\), and the system shifts toward the products because decreasing the temperature decreases the total gas pressure, which shifts the equilibrium to the side with more moles of gas.
- **B.** \(Q_p < K_p\), and the system shifts toward the products because lowering the temperature increases the value of \(K_p\) for an endothermic reaction.
- **C.** \(Q_p > K_p\), and the system shifts toward the reactants because the value of \(K_p\) decreases at the lower temperature while \(Q_p\) initially remains equal to the original equilibrium constant.
- **D.** \(Q_p > K_p\), and the system shifts toward the reactants because the partial pressure of \(\text{NO(g)}\) decreases by a larger percentage than the partial pressures of \(\text{N}_2\text{(g)}\) and \(\text{O}_2\text{(g)}\) upon cooling.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/120290/*