Question

Write a short note on Vapour pressure.

Answer 1

1. Molecules of liquid have a tendency to escape from its surface to form vapour above it. This is called evaporation.
2. When a liquid is placed in a closed container, the liquid undergoes evaporation, and the vapours formed undergo condensation.
3. At equilibrium, the rate of evaporation and the rate of condensation are equal.
4. The pressure exerted by the vapour in equilibrium with the liquid is known as saturated vapour pressure or simply vapour pressure.
5. Vapour pressure is measured by means of a manometer.
6. The most common unit for vapour pressure is the torr. 1 torr = 1 mm Hg.