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Ch.15 - Chemical Equilibrium
Chapter 15, Problem 7b

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. There will be less PbO2 remaining in vessel B,

Verified step by step guidance
1
Step 1: Understand the chemical reaction involved. The decomposition of lead(IV) oxide (PbO_2) into lead(II) oxide (PbO) and oxygen gas (O_2) is given by the equation: 2 PbO_2(s) ⇌ 2 PbO(s) + O_2(g).
Step 2: Recognize that the reaction is at equilibrium. At equilibrium, the rate of the forward reaction (decomposition of PbO_2) equals the rate of the reverse reaction (formation of PbO_2 from PbO and O_2).
Step 3: Consider the effect of temperature. Both vessels are heated to 400°C, which is above the decomposition temperature of PbO_2, allowing the reaction to proceed towards equilibrium.
Step 4: Analyze the initial conditions in both vessels. If vessel B initially contains more PbO_2 than vessel A, the amount of PbO_2 that decomposes will depend on the initial amount present and the equilibrium constant at 400°C.
Step 5: Apply Le Chatelier's Principle. If vessel B has a different initial condition (e.g., more PbO_2), the system will adjust to reach equilibrium, potentially resulting in different amounts of PbO_2 remaining compared to vessel A.

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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 towards the products (PbO and O2), thus reducing the amount of PbO2 present.
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Equilibrium Constant (K)

The equilibrium constant (K) quantifies 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 value of K will change with temperature, influencing how much PbO2 remains in each vessel after heating. A higher temperature typically increases K for endothermic reactions, indicating more products are formed.
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Effect of Temperature on Reaction Rates

Temperature affects the rate of chemical reactions, with higher temperatures generally increasing reaction rates. In the case of the decomposition of PbO2, heating to 400°C accelerates the reaction, leading to a faster conversion of PbO2 to PbO and O2. This increased rate of reaction is crucial for understanding why vessel B, if designed differently (e.g., with more surface area or different conditions), may have less PbO2 remaining compared to vessel A.
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