If K = 1, what can be said about equilibrium?

If K = 1, what can be said about equilibrium?

• A. The reaction strongly favors products
• B. The concentrations of products and reactants are equal
• C. The reverse reaction dominates
• D. The system cannot reach equilibrium

Answer: (B)

The equilibrium constant tells you how the concentrations on either side of the reaction balance at equilibrium. For a simple one-to-one reaction A ⇌ B, K equals the concentration of B divided by the concentration of A. If K is 1, that ratio is 1, so the concentrations of products and reactants are equal at equilibrium. This also means the forward and reverse reaction rates are equal at that point. Note the nuance: if the reaction involves different stoichiometric coefficients (for example A2 ⇌ 2A), K = [A]^2/[A2]. Then K = 1 would imply [A] ≠ [A2] in general (specifically [A] = sqrt([A2])), so equal concentrations would not necessarily hold. But for the common 1:1 case, K = 1 indeed corresponds to equal concentrations on both sides.

The equilibrium constant tells you how the concentrations on either side of the reaction balance at equilibrium. For a simple one-to-one reaction A ⇌ B, K equals the concentration of B divided by the concentration of A. If K is 1, that ratio is 1, so the concentrations of products and reactants are equal at equilibrium. This also means the forward and reverse reaction rates are equal at that point.

Note the nuance: if the reaction involves different stoichiometric coefficients (for example A2 ⇌ 2A), K = [A]^2/[A2]. Then K = 1 would imply [A] ≠ [A2] in general (specifically [A] = sqrt([A2])), so equal concentrations would not necessarily hold. But for the common 1:1 case, K = 1 indeed corresponds to equal concentrations on both sides.