But not all particles have the same kinetic energy, they have a distribution of energies. Some particles in a liquid or solid may have enough kinetic energy to break the chemical bonds and leave the substance . The liquid is evaporating and the solid is subliming. When the particles with the highest kinetic energy leave the substance, the average kinetic energy of the remaining particles decreases. The temperature of the substance therefore decreases.
Evaporation cools the substance.
Relative Humidity Molecules can leave liquid water through evaporation, but molecules also can reenter the liquid water if there is water vapor in the surrounding air. We call this phenomenon condensation . The relative humidity is the ratio of the rate of condensation to the rate of evaporation. The relative humidity depends on the temperature and on the density of the water vapor in the air. The higher the temperature, the higher is the average kinetic energy of the molecules and therefore the rate at which they are leaving.