What occurs during the phase transition of a substance at its boiling point?

During the phase transition of a substance at its boiling point, the substance remains at a constant temperature despite the input of heat. This is because the energy added is used to break the intermolecular forces that hold the molecules in a liquid state, rather than increasing the temperature of the substance. At the boiling point, the transition from liquid to gas occurs, and thermal energy is utilized for this phase change.

This phenomenon is due to the nature of phase transitions, wherein the temperature stabilizes while the substance undergoes a change in state, such as from liquid to vapor. The thermal energy absorbed during this time increases the potential energy of the molecules, allowing them to escape the liquid phase and enter the gaseous phase. This constant temperature characteristic is a fundamental property of boiling and is distinctly different from the behavior of substances undergoing other types of processes, such as heating or cooling without a phase change.