Question

How do intermolecular forces affect vapor pressure?

Answer 1

The relation between vapor pressure and intermolecular forces is quite simple. Vapor pressure is inversely proportional to the intermolecular forces. Stronger the intermolecular forces lower will be the vapor pressure and vice versa.

Complete step by step answer:
In a state of equilibrium, the pressure which is exerted by the vapor molecules on a solid or liquid surface is called its vapor pressure. Vapor pressure of liquid is inversely proportional to the intermolecular forces between the atoms of liquid. This relation takes place as if the liquid has stronger intermolecular forces than the rate of evaporation of liquid will be very low and hence it causes lower vapor pressure. Similarly, if the liquid has weak intermolecular forces then the rate of evaporation of liquid will be very high and hence it causes higher vapor pressure.
We can also say more precisely, that the vapour molecules come into the liquid phase and liquid molecules come into the vapour phase. Suppose that the intermolecular forces between the liquid molecules are strong so it will not easily leave the liquid phase and that’s why it reduces the vapour pressure and also its boiling point will be higher. And if the intermolecular forces between the liquid molecules are weak they will easily leave the liquid phase and enter the vapour phase and hence have low boiling points.

Note:
Each and every liquid has a different vapour pressure. This difference is due to the intermolecular forces such as London dispersion forces, hydrogen bonds, dipole-dipole forces and so on. If the intermolecular forces are strong, the vapor pressure will be low and vice versa.