Equilibrium – Solutions

1)  A liquid is in equilibrium with its vapour in a sealed container at a fixed temperature.

The volume of the container is suddenly increased.

1. a) What is the initial effect of the change on vapour pressure?
2. b) How do rates of evaporation and condensation change initially?
3. c) What happens when equilibrium is restored finally and what will be the final vapour pressure?

Solution

a) Due to increase in the volume, there will be decrease in the vapour pressure of the liquid because vapours now would be disturbed over larger space, that is due to increase in volume.

b) The rate of evaporation will increase due to the increase in the surface area of liquid and hence more space is available for the molecules to escape. The rate of condensation will decrease due to decrease in the number of vapour molecules in unit volume with increase in volume.