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Ch.15 - Chemical Equilibrium
All textbooksMcMurry 8th EditionCh.15 - Chemical EquilibriumProblem 53
Chapter 15, Problem 53

Identify the true statement about the concentrations of A and B once the reaction A ⇌ B has reached equilibrium. (a) The concentration of A equals the concentration of B. (b) The concentrations of A and B are constant. (c) The concentration of A decreases and the concentration of B increases. (d) The concentration of B decreases and the concentration of A increases.

Verified step by step guidance
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Step 1: Understand the concept of chemical equilibrium. At equilibrium, the rate of the forward reaction equals the rate of the reverse reaction, meaning the concentrations of reactants and products remain constant over time.
Step 2: Analyze each statement in the context of equilibrium. Statement (a) suggests that the concentrations of A and B are equal, which is not necessarily true at equilibrium unless the equilibrium constant dictates it.
Step 3: Evaluate statement (b). At equilibrium, the concentrations of A and B are indeed constant, as the rates of the forward and reverse reactions are equal.
Step 4: Consider statement (c). This describes a scenario where the reaction is still proceeding towards equilibrium, not a state of equilibrium itself.
Step 5: Assess statement (d). Similar to statement (c), this describes a non-equilibrium state where the reaction is still shifting towards equilibrium.

Key Concepts

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

Chemical Equilibrium

Chemical equilibrium occurs in a reversible reaction when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. At this point, the system is in a dynamic state where the concentrations do not change over time, even though both reactions continue to occur.
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Concentration in Equilibrium

At equilibrium, the concentrations of reactants and products remain constant, but they do not have to be equal. This means that while the amounts of A and B may differ, their concentrations will stabilize at specific values determined by the reaction conditions and the equilibrium constant.
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Le Chatelier's Principle

Le Chatelier's Principle states that if a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the system will adjust to counteract that change and restore a new equilibrium. This principle helps predict how the concentrations of A and B will respond to external changes, but it does not imply that their concentrations will be equal.
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Related Practice
Textbook Question

The following pictures represent the initial and equilibrium states for the exothermic decomposition of gaseous A mol- ecules (red) to give gaseous B molecules (blue). (a) Write a balanced chemical equation for the reaction.

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Textbook Question

The following pictures represent the initial and equilibrium states for the exothermic reaction of solid A (red) with gas- eous B2 (blue) to give gaseous AB. (a) Write a balanced chemical equation for the reaction.

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Textbook Question
Identify the true statement about the rate of the forward and reverse reaction once a reaction has reached equilibrium. (a) The rate of the forward reaction and the reverse reaction is zero. (b) The rate of the forward reaction is greater than the rate of the reverse reaction. (c) The rate of the reverse reaction is greater than the rate of the forward reaction. (d) The rate of the forward reaction is equal to the rate of the reverse reaction.
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Textbook Question
For each of the equilibria in Problem 15.56, write the equi-librium constant expression for Kp and give the equation that relates Kp and Kc. (a)
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