If Kc = 1, which statement is true?

• A. Only products are present.
• B. Only reactants are present.
• C. Significant amounts of both reactants and products at equilibrium.
• D. The reaction has not reached equilibrium.

Answer: (C)

Kc tells you how the concentrations of products and reactants compare at equilibrium. When Kc equals 1, the concentrations are balanced in the sense that the product term and the reactant term in the expression are equal, so neither side dominates. This means you have appreciable amounts of both reactants and products present at equilibrium. It isn’t a non-equilibrium state; it’s simply a situation where the forward and reverse tendencies are balanced. If you had mostly products, Kc would be much greater than 1; if you had mostly reactants, Kc would be much less than 1.