And this pressure is called vapor pressure. So vapor pressure, by definition, is the pressure exerted by gas molecules that are in equilibrium with their liquid or solid state. And at this point, the rate of molecules leaving the solid or liquid state is equal to the rate at which they enter that state. Now, from everyday experience, we know a hot liquid will evaporate quicker than a cold liquid. And this is because vapor pressure is related to kinetic energy and temperature. This equation shows exactly that.