A liquid is in equilibrium with its vapour in a sealed container at a fixed temperature. The volume of the container is suddenly increased.
(i) What is the initial effect of the change on vapour pressure?

(ii) How do rates of evaporation and condensation change initially?

(iii) What happens when equilibrium is restored finally and what will be the final vapour pressure?

(i) Vapour pressure will decrease initially.
(ii) The rate of evaporation remains constant at a temperature in a closed vessel. However, the rate of condensation will be low initially due to the presence of lesser molecules per unit volume in the vapour phase and hence the number of collisions per unit time with the liquid surface decreases.
(iii) When equilibrium is restored finally, then the rate of evaporation becomes equal to the rate of condensation. The final vapour pressure will be the same as it was initial.