Why Does Vapor Pressure change with Temperature?
Vapor pressure describes the pressure exerted above a liquid (or solid in the case of sublimation) by a vapor during the phase of evaporation. To understand vapor pressure and temperature, you need to understand kinetic energy. Kinetic energy is an object’s extra motion. Think of a roller coaster. When the cars approach the top, they are building potential energy. As the roller coaster falls forward through the drop and reaches the bottom of the hill, it achieves maximum kinetic energy. What does this have to do with vapor pressure?
Imagine a covered pot of water on a stove, before you have turned on the burner. Water in the liquid phase is attempting to remain in equilibrium with the water vapor in the air above it. It is successful since the rate of exchange of liquid to gas and vice versa is equal.
This changes when you turn the burner on, increasing the temperature. Heat increases the amount of kinetic energy of water in both states. This makes it difficult for the vapor to condense to form the liquid because the heat makes the molecules bounce apart. However, it makes it easier for the liquid molecules to come apart. Liquid continuously builds until, finally, the molecules are so crowded that condensation becomes as fast as the evaporation process. This force is the vapor pressure. When the vapor pressure increases so that it has the same pressure as the atmospheric pressure, the liquid reaches its boiling point.