It should be apparent that the changes between vapor and liquid states are related to the kinetic energy values of the molecules. In order for a molecule of liquid water to evaporate it must have a sufficient value of kinetic energy. The kinetic energy of the molecules will increase with temperature by definition. As a result, the maximum amount of water vapor that can possibly be present in air will increase with temperature. As temperature rises, so does kinetic energy .
More molecules have sufficient energy to evaporate into water vapor .
So saturation vapor pressure is proportional to temperature The relationship between temperature, kinetic energy, and saturation vapor pressure, can be examined by looking at how the distribution of kinetic energy for molecules of a gas changes with temperature. Figure 2 illustrates the distribution of molecular kinetic energies at two values of temperature. These distributions can be theoretically calculated, and are called Maxwell Distributions. Distribution of Molecular Kinetic Energy as a Function of Temperature Figure 2 Distribution of molecular velocities as related to temperature Note that the warmer temperature is associated with higher values of kinetic energy. At higher temperatures more molecules of water will have sufficient kinetic energy to exist in as water vapor.