vapour pressure of gas

The pressure exerted by the molecules of vapour on the surface of liquid at equilibrium is called vapour pressure.
It is just called equilibrium constant.

Remember :-Pressure depends on temperature and nature of liquid.

Nature of liquid means liquid is either volatile nature or non-volatile nature.
If liquid is volatile then the vapour pressure is more than that of non-volatile liquid at same temperature.

Remember : Vapour pressure do not depend on amount of liquid as well as surface area of liquid.

Vapour pressure increases with increase in temperature.

When a non-volatile solute is added to a pure solvent, the vapour pressure of resulting solution decreases. This is due to lower or smaller availibility of molecules of solvent on the surface as compare to that of pure liquid.

The vapour pressure of solution containing non-volatile solute is directly proportional to mole fraction of solvent.

At 25^o C, vapour pressure of water (H₂O) is 23.8 torr.

Vapour pressure of solution is product of vapour of pure solvent and mole fraction of solvent in the solution.