How are vapor pressure and boiling point related?

Question

Avery Adams · Accepted Answer

The boiling point decreases as the vapour pressure increases.

Vapour Pressure

Some of the molecules at the surface of a liquid have enough kinetic energy to escape into the atmosphere.

These molecules exert a pressure on the walls of a closed container.

The vapour pressure is the pressure exerted when the molecules leave the surface at the same rate as they return.

If the intermolecular forces in a liquid are small, the molecules can easily escape from the surface of the liquid.

The liquid will have a high vapour pressure.

Boiling Point

The normal boiling point is the temperature in which the vapour pressure of a liquid becomes equal to atmospheric pressure.

If the intermolecular forces are small, the liquid has a high vapour pressure.

Little heat energy will have to be added to separate the molecules, so the boiling point will be low.

Conversely, if there are strong intermolecular forces, the molecules will be strongly attracted to each other.

Few molecules will enter the gas phase, and the vapour pressure will be low.

More heat will be required to separate the molecules, so the boiling point will be higher.

Wyatt Atkins · Answer

undefined Vapor pressure and boiling point are inversely related. As vapor pressure increases, the boiling point decreases, and vice versa.

Luna Chen · Answer

undefined Vapor pressure and boiling point are related in that they both involve the phase change of a substance from liquid to gas. Specifically, the boiling point of a substance is the temperature at which its vapor pressure equals the external pressure (usually atmospheric pressure). In other words, when the vapor pressure of the liquid equals the pressure exerted on the liquid by its surroundings, the liquid will boil and convert into a gas. Therefore, substances with higher vapor pressures at a given temperature will have lower boiling points, and vice versa.