Now, if the kinetic energy is high enough, they could escape the liquid phase and become a gas molecule. And this is called evaporation. Condensation is the opposite. It's the process by which gas molecules hitting the surface of the liquid get stuck in the liquid. Now, when the rates of evaporation equal condensation, the state is an equilibrium. And when the state is in the equilibrium, we can measure the pressure exerted by the gas molecules on the wall of the container.