Evaporation and boiling are both processes in which water vapor is eliminated from liquid, converting it from a liquid phase to a gaseous phase. Both are physical changes as the chemical composition remains the same in the liquid and gaseous phases. Both processes require some form of energy, usually thermal energy but other forms of energy that increase the kinetic energy of the molecules can also bring about evaporation or boiling. Both processes are dependent on external conditions such as humidity, air pressure and temperature (of the air or liquid).