In this educational resource you can check the next physical phenomenon: when there is a change of state in pure substances, the temperature remains constant.

The educational resource shows an interactive animation about the equilibrium between different states: a substance (water, for example) in different states at different temperatures (ice and water) will eventually reach an equilibrium temperature.

The educational resource shows an interactive animation about the change of phase: solids melt when they are heated and liquids evaporate, changing to a gaseous state. If you increase the vibration of the molecules you can see how water changes phase.