$A$ 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?

(N/A) Initially,the vapour pressure will decrease because the volume increases,which causes the concentration of vapour to decrease.
$(b)$ The rate of evaporation remains constant at a constant temperature. However,the rate of condensation decreases initially because there are fewer molecules per unit volume in the vapour phase to collide with the liquid surface.
$(c)$ When equilibrium is restored,the rate of evaporation becomes equal to the rate of condensation. The final vapour pressure will be the same as it was originally at that temperature.