Vapour pressure decreases with increase in polarity of liquid molecules.
What is vapour pressure?
Vapour pressure is defined as a measure of the tendency of a material to change its state to solid/liquid to gas or vapour when the temperature increases. It indicates the rate of evaporation of liquid. It is also closely related to the tendency of particles to escape from the liquid or solid-state.
- The vapour pressure is a measurement of how much pressure a gas exerts over a liquid in a sealed container.
- The strength of a liquid’s intermolecular forces determines its vapour pressure.
- The vapour pressure of a liquid with weak intermolecular forces is higher.
- The vapour pressure of a liquid with stronger intermolecular forces is lower than that of a liquid with weaker intermolecular forces.
- Diethyl ether, for example, is a nonpolar liquid with weak dispersion forces. It has a vapour pressure of 58.96 kPa at 20°C.
- Water is a polar liquid with relatively heavy hydrogen bonding that attracts the molecules together. Water has a vapour pressure of 2.33 kPa at 20°C, which is much lower than diethyl ether.