Ch.15 - Chemical Equilibrium

Problem 8c

Chapter 15, Problem 8c

When lead(IV) oxide is heated above 300°C, it decomposes according to the reaction, 2 PbO₂(𝑠)⇌2PbO(𝑠)+O2(𝑔). Consider the two sealed vessels of PbO₂ shown here. If both vessels are heated to 400°C and allowed to come to equilibrium, which of the following statements is or are true? c. The partial pressure of O2(𝑔) will be the same in vessels A and B. [Section 15.4]

Verified step by step guidance

Identify the chemical reaction involved: 2 PbO2(s) ⇌ 2 PbO(s) + O2(g). This is a decomposition reaction where lead(IV) oxide decomposes into lead(II) oxide and oxygen gas.

Understand the concept of equilibrium: At equilibrium, the rate of the forward reaction equals the rate of the reverse reaction, and the concentrations of reactants and products remain constant.

Consider the conditions given: Both vessels are heated to 400°C, which is above the decomposition temperature of PbO2, allowing the reaction to proceed until equilibrium is reached.

Recognize that the partial pressure of a gas at equilibrium depends on the equilibrium constant and the initial conditions. Since both vessels are sealed and contain the same substance, the equilibrium constant for the reaction will be the same in both vessels.

Conclude that if the initial amounts of PbO2 are the same in both vessels, the partial pressure of O2(g) at equilibrium will be the same in both vessels, as the equilibrium position is determined by the same reaction conditions and equilibrium constant.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Le Chatelier's Principle

Le Chatelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change. In the context of the decomposition of lead(IV) oxide, increasing the temperature will favor the endothermic reaction, shifting the equilibrium to produce more O2 gas.

Equilibrium Constant (K)

The equilibrium constant (K) is a numerical value that expresses the ratio of the concentrations of products to reactants at equilibrium for a given reaction at a specific temperature. For the decomposition of PbO2, the K value will change with temperature, affecting the concentrations of PbO and O2 in the sealed vessels.

Partial Pressure

Partial pressure is the pressure exerted by a single component of a gas mixture. In the context of the question, the partial pressure of O2 in both vessels A and B will depend on the amount of O2 produced at equilibrium, which should be the same if both vessels are identical and reach the same equilibrium state at 400°C.

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Related Practice

Textbook Question

Ethene (C₂H₄) reacts with halogens (X₂) by the following reaction:

C₂H₄(𝑔) + X₂(𝑔) ⇌ C₂H₄X₂(𝑔)

The following figures represent the concentrations at equilibrium at the same temperature when X₂ is Cl₂ (green), Br₂ (brown), and I₂ (purple). List the equilibria from smallest to largest equilibrium constant. [Section 15.3]

Textbook Question

When lead(IV) oxide is heated above 300°C, it decomposes according to the reaction, 2 PbO2(𝑠) ⇌ 2PbO(𝑠) + O2(𝑔). Consider the two sealed vessels of PbO2 shown here. If both vessels are heated to 400°C and allowed to come to equilibrium, which of the following statements is or are true? a. There will be less PbO2 remaining in vessel A than in vessel B.

Textbook Question

When lead(IV) oxide is heated above 300°C, it decomposes according to the reaction, 2 PbO₂(𝑠)⇌2PbO(𝑠)+O2(𝑔). Consider the two sealed vessels of PbO₂ shown here. If both vessels are heated to 400°C and allowed to come to equilibrium, which of the following statements is or are true?

b. The solid left at the bottom of each vessel will be a mixture of PbO₂(𝑠) and PbO(𝑠).

Textbook Question

The reaction A₂ + B₂ ⇌ 2 AB has an equilibrium constant K_c = 1.5. The following diagrams represent reaction mixtures containing A₂ molecules (red), B₂ molecules (blue), and AB molecules. (a) Which reaction mixture is at equilibrium?

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Textbook Question

The diagram shown here represents the equilibrium state for the reaction A2(𝑔) + 2B(𝑔) ⇌ 2AB(𝑔). (a) Assuming the volume is 2 L, calculate the equilibrium constant 𝐾𝑐 for the reaction.

Textbook Question

Suppose that the gas-phase reactions A → B and B → A are both elementary reactions with rate constants of 4.7×10⁻³ s⁻¹ and 5.8×10⁻¹ s⁻¹, respectively. (a) What is the value of the equilibrium constant for the equilibrium A(g) ⇌ B(g)? (b) Which is greater at equilibrium, the partial pressure of A or the partial pressure of B?