Question

Consider the reaction:

A (aq) + B(aq) <--> C (aq) + D (aq) + E (aq),
already at equilibrium. Addition of water to the reaction mixture (select the best answer).
a. it is impossible to predict the effect of water addition.
b. will disturb the equilibrium. The reaction will shift right, toward products.
c. will have no effect on the equilibrium, because [H2O] is not included in the equilibrium constant, K.
d. will disturb the equilibrium. The reaction will shift left, toward reactants.

Answer 1

Adding water to a reaction mixture at equilibrium dilutes the concentrations of the reactants and products and causes the system to shift right towards products to re-establish equilibrium, as it compensates for the dilution. Option b is correct.

Step-by-step explanation:

When water is added to a reaction mixture that is already at equilibrium, it can affect the reaction depending on the nature of the system. For reactions where water is a solvent and its concentration is not included in the expression for the equilibrium constant (K), adding water typically increases the volume of the solution and dilutes the concentrations of the reactants and products.

According to Le Châtelier's principle, the system will respond to this stress to re-establish equilibrium, most likely by shifting in the direction that compensates for the dilution. In the given reaction A (aq) + B(aq) ⇌ C (aq) + D (aq) + E (aq), adding water would dilute all aqueous species.

Because water is not included in the equilibrium constant for such reactions, the system attempts to counteract the dilution and will likely shift to the right towards product formation to reach a new equilibrium state.