Ch.15 - Chemical Equilibrium

McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook

McMurry 8th Edition

Ch.15 - Chemical Equilibrium

Problem 46

Chapter 15, Problem 46

The following pictures represent the composition of the equi- librium mixture for the reaction A + B ∆ AB at 300 K and at 400 K.
Is the reaction exothermic or endothermic? Explain using Le Châtelier's principle.

Verified step by step guidance

Step 1: Identify the reaction and the components involved: A + B ⇌ AB.

Step 2: Observe the molecular representations at 300 K and 400 K. Note the number of reactants (A and B) and products (AB) at each temperature.

Step 3: Compare the concentrations of reactants and products at the two temperatures. At 300 K, there are more AB molecules compared to 400 K.

Step 4: Apply Le Châtelier's principle: If the concentration of products decreases with an increase in temperature, the reaction shifts to the left (towards reactants) to counteract the change.

Step 5: Conclude that the reaction is exothermic because increasing the temperature shifts the equilibrium towards the reactants, indicating that heat is a product of the reaction.

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Key Concepts

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

Chemical Equilibrium

Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. In the context of the reaction A + B ⇌ AB, the equilibrium position can shift based on changes in temperature, pressure, or concentration, affecting the amounts of A, B, and AB present in the mixture.

Le Châtelier's Principle

Le Châtelier's principle states that if a dynamic equilibrium is disturbed by changing the conditions, the system will adjust to counteract the change and restore a new equilibrium. For example, if the temperature of an exothermic reaction is increased, the equilibrium will shift to favor the reactants, while a decrease in temperature will favor the formation of products.

Exothermic vs. Endothermic Reactions

Exothermic reactions release heat to the surroundings, resulting in an increase in temperature, while endothermic reactions absorb heat, leading to a decrease in temperature. The nature of the reaction can be inferred from the effect of temperature changes on the equilibrium position, where an increase in temperature favors the endothermic direction and a decrease favors the exothermic direction.

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Related Practice

Textbook Question

The reaction A2 + B ∆ A + AB has an equilibrium con-stant Kc = 2. The following pictures represent reaction mix- tures that contain A atoms (red), B atoms (blue), and A2 and AB molecules.

(a) Which reaction mixture is at equilibrium?

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Textbook Question

The following pictures represent the initial state and the equilibrium state for the reaction of A₂ molecules (red) with B atoms (blue) to give AB molecules. (a) Write a balanced chemical equation for the reaction.

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Textbook Question

Consider the reaction A + B ∆ AB. The vessel on the right contains an equilibrium mixture of A molecules (red spheres), B molecules (blue spheres), and AB molecules. If the stopcock is opened and the contents of the two vessels are allowed to mix, will the reaction go in the forward or reverse direction? Explain.

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Textbook Question

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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Textbook Question

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