Which of the following statements will always apply when a reversible chemical reaction has attained equilibrium?

(1) All reactants will convert to products

(2) The reaction proceeds alternately in the forward and reverse directions

(3) The Gibbs free energy of the system reaches a minimum,

(4) The forward reaction will dominate over the reverse reaction

(3) The Gibbs free energy of the system reaches a minimum.

When a reversible chemical reaction reaches equilibrium, the following principles apply:

(Incorrect) All reactants will convert to products → This is false because, at equilibrium, both reactants and products are present in a dynamic balance. Some amount of reactants usually remains unreacted.
(Partially Correct) The reaction proceeds alternately in the forward and reverse directions → While the reaction does continue in both directions, it happens simultaneously rather than alternately. The rates of the forward and reverse reactions become equal, leading to a dynamic equilibrium.
(Correct) The Gibbs free energy of the system reaches a minimum → At equilibrium, the Gibbs free energy (G) is at its lowest possible value under the given conditions. This means the system is in a state of maximum stability and no net energy is available to drive the reaction in either direction.
(Incorrect) The forward reaction will dominate over the reverse reaction → At equilibrium, the rates of the forward and reverse reactions are equal, so neither dominates the other. The concentrations of reactants and products remain constant over time.

The defining condition of equilibrium is that Gibbs free energy is at its minimum, making option (3) the correct choice.