A liquid is in equilibrium with its vapour in a sealed container at a fixed temperature. The volume of the container is suddenly increased.
a. what is the initial effect of the change on vapour pressure?
b. How do rates of evaporation and condensation change initially?
c. What happens when equilibrium is restored finally and what will be the final vapour pressure?

Explanation

(a) Initially the vapour pressure will increase.
(b) The rate of evaporation will remain constant at constant temperature in closed vessel. However, rate of condensation will be low initially because there are lesser number of molecules per unit volume in the vapour phase. Therefore, the number of collisions per unit volume with the liquid surface decreases.
(c) When equilibrium is restored, rate of evaporation becomes equal to rate of condensation. The final vapour pressure will be same as it was originally.