During an experiment, distilled water was placed in a sealed container and the container was heated gradually. Describe this system when it reaches phase equilibrium.

As the container was heated up gradually, more and more liquid water is turned into water vapor, a gas. The pressure inside went up with the temperature. High pressure causes some water vapor to turn back into liquid. At phase equilibrium, liquid water is turned into water vapor gas as quickly as water vapor is turned back into liquid water.