Ch.15 - Chemical Equilibrium

Problem 48

Chapter 15, Problem 48

The following picture represents the composition of the equi- librium mixture for the endothermic reaction A2 ∆ 2 A at 500 K. Draw a picture that represents the equilibrium mixture after each of the following changes.(b) Increasing the volume

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Identify the initial equilibrium mixture (image (i)) where the reaction A2 ⇌ 2A is at equilibrium.

Recognize that increasing the volume of the system will decrease the pressure.

According to Le Chatelier's principle, the system will shift to counteract this change by favoring the side with more gas molecules.

In this case, the reaction will shift towards the production of more A atoms (since 2A has more molecules than A2).

Draw the new equilibrium mixture (image (ii)) showing an increased number of A atoms and a decreased number of A2 molecules.

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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 reaction A2 ⇌ 2A, increasing the volume of the system will favor the side with more moles of gas, which in this case is the product side (2A), thus shifting the equilibrium to the right.

Endothermic Reactions

An endothermic reaction is one that absorbs heat from its surroundings. In the reaction A2 ⇌ 2A, the forward reaction is endothermic, meaning that increasing the temperature will also favor the formation of products. Understanding this concept is crucial when predicting how changes in temperature and volume affect the equilibrium position.

Equilibrium Mixture

An equilibrium mixture refers to the state in a reversible reaction where the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. In the given reaction, the equilibrium mixture at 500 K consists of both A2 and A, and any changes in conditions, such as volume, will alter the concentrations of these species until a new equilibrium is established.

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Textbook Question

The following pictures represent the composition of the equi- librium mixture for the reaction A + B ∆ AB at 300 K and at 400 K.

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The following picture represents the equilibrium state for the reaction 2 AB ∆ A2 + B2. Which rate constant is larger, kf or kr? Explain.

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Textbook Question

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