Which of the following statements will apply when a reversible chemical reaction has attained equilibrium? A The Gibbs free energy of the system reaches a minimum B All reactants will convert to product C The reaction proceeds alternately in the forward and reverse directions D The forward reaction will dominate over reverse reaction
The correct answer and explanation is:
Correct Answer: A) The Gibbs free energy of the system reaches a minimum
Explanation (300 words):
In a reversible chemical reaction, equilibrium is the state where the rate of the forward reaction equals the rate of the reverse reaction, and the concentrations of reactants and products remain constant over time. It does not mean the reactions stop, but rather that the changes occur at the same rate in both directions, maintaining a dynamic balance.
Let’s analyze the options:
- A) The Gibbs free energy of the system reaches a minimum
✅ This is the correct answer. At equilibrium, the system has no further net tendency to change. Thermodynamically, this is the point where the Gibbs free energy (ΔG) is at its lowest possible value under the given conditions (constant temperature and pressure). At this point, ΔG = 0, meaning the system is at maximum stability, and no net work can be extracted. - B) All reactants will convert to product
❌ False. In a reversible reaction at equilibrium, both reactants and products are present. The system does not necessarily convert all reactants into products unless the reaction lies completely to the right (very rare). - C) The reaction proceeds alternately in the forward and reverse directions
❌ Misleading. Reactions don’t proceed “alternately” but simultaneously in both directions. At equilibrium, both reactions are ongoing at equal rates, not in turn. - D) The forward reaction will dominate over reverse reaction
❌ Incorrect. At equilibrium, the forward and reverse reactions occur at the same rate, so neither dominates. If one dominated, the system wouldn’t be at equilibrium.
Summary:
At equilibrium, the system is thermodynamically stable, and Gibbs free energy is minimized. The concept is crucial in chemistry and biology, ensuring reactions proceed only until they reach this stable state.