Ch.4 - Reactions in Aqueous Solution

Problem 4

Chapter 4, Problem 4

The concept of chemical equilibrium is very important. Which one of the following statements is the most correct way to think about equilibrium? (a) If a system is at equilibrium, nothing is happening. (b) If a system is at equilibrium, the rate of the forward reaction is equal to the rate of the back reaction. (c) If a system is at equilibrium, the product concentration is changing over time.

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Understand that chemical equilibrium is a dynamic state where the concentrations of reactants and products remain constant over time.

Recognize that at equilibrium, the forward and reverse reactions continue to occur, but at equal rates, so there is no net change in concentrations.

Evaluate statement (a): It suggests that nothing is happening, which is incorrect because reactions are still occurring at equilibrium.

Evaluate statement (b): It correctly describes equilibrium as the point where the rate of the forward reaction equals the rate of the reverse reaction.

Evaluate statement (c): It incorrectly suggests that product concentration changes over time, which contradicts the definition of equilibrium.

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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 in a reversible reaction when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products over time. This state does not imply that the reactions have stopped; rather, they continue to occur at equal rates.

Dynamic Nature of Equilibrium

Equilibrium is dynamic, meaning that even though the concentrations of reactants and products remain constant, the individual molecules are still reacting. This ongoing process is crucial for understanding that equilibrium is not a static state but a balance of continuous activity.

Equilibrium Constant

The equilibrium constant (K) quantifies the ratio of product concentrations to reactant concentrations at equilibrium, each raised to the power of their coefficients in the balanced equation. This constant provides insight into the position of equilibrium and the extent of the reaction, indicating whether products or reactants are favored.

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Equilibrium Constant K

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