Final answer:
Doubling the concentration of a reactant in a reversible chemical reaction at equilibrium does not affect the equilibrium constant, as it is a fixed value specific to the reaction at a given temperature. Instead, the system shifts to re-establish equilibrium with a new concentration of reactants and products.
Step-by-step explanation:
In a reversible chemical reaction at equilibrium, doubling the concentration of a reactant does not change the equilibrium constant (Keq). The Keq is a fixed value for a given reaction at a specific temperature, representing the ratio of the concentrations of products to reactants, with each raised to the power of their respective coefficients in the balanced equation. When the concentration of a reactant is increased, the system will shift to re-establish equilibrium according to Le Chatelier's Principle, but the value of Keq remains constant.
For example, consider the reaction H₂(g) + I₂(g) ⇒ 2HI(g) with an equilibrium constant Kc = 50.0 at 400 °C. If the concentration of HI is doubled, the rate of the reverse reaction will increase, but this does not affect the equilibrium constant itself. Instead, the system will eventually reach a new equilibrium position with different concentrations of reactants and products, yet the value of Keq will still be 50.0.
It is also noteworthy that if the chemical equation is written in reverse, the equilibrium constant expression will be the reciprocal of the forward reaction. However, regardless of how the reaction is approached, the actual numerical value of the equilibrium constant for a given reaction at a particular temperature does not change with the concentration of reactants or products.