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Difficulty: MediumReversible Reactions and Dynamic Equilibrium

Which of the following statements correctly describes a chemical reaction system that has attained dynamic equilibrium in a closed vessel?

  1. The rates of the forward and reverse reactions are equal, and the concentrations of reactants and products remain constant.Answer
  2. B
    The addition of a positive catalyst increases the net equilibrium yield of the forward reaction products.
  3. C
    All chemical activity ceases completely once the concentrations of reactants and products become equal.
  4. D
    The total molar concentration of the products must equal the total molar concentration of the reactants.

Answer

The correct statement is that the rates of the forward and reverse reactions are equal, while the concentrations of reactants and products remain constant.
Dynamic chemical equilibrium is defined by equal rates of the forward and reverse reactions in a closed system. Because reactants are converted to products at the exact same speed that products revert back to reactants, the macroscopic concentrations of all participating species remain constant over time.

Step-by-Step Solution

1
Define dynamic equilibrium in chemical systems.
Dynamic equilibrium occurs in a closed system when a reversible reaction proceeds in opposite directions at identical speeds.
Understanding the dynamic nature distinguishes chemical equilibrium from static equilibrium.
2
Analyze macroscopic versus microscopic behavior.
Microscopically, forward and reverse processes continuously take place; macroscopically, measurable parameters such as concentration, pressure, and color remain unvarying.
Equal rates mean the formation rate of any species equals its consumption rate.
3
Evaluate option statements against dynamic equilibrium criteria.
The statement asserting equal reaction rates and constant concentrations aligns perfectly with dynamic equilibrium principles.
This directly satisfies the fundamental definition.

Key Concept

Characteristics of Dynamic Chemical Equilibrium
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Topics

Reversible Reactions and Dynamic Equilibrium