Why are the freezing point and melting point of a substance the same temperature?

The freezing point and melting point of a substance are the same temperature due to the concept of equilibrium between solid and liquid phases at that specific temperature. At this temperature, a substance can exist as both a solid and a liquid simultaneously. When the temperature of a substance reaches its melting point, solid particles gain enough energy to overcome intermolecular forces and enter the liquid phase. Conversely, at the freezing point, the liquid particles lose energy, allowing them to form stable intermolecular bonds and enter the solid phase.

This balance between the two states at a specific temperature allows the substance to transition back and forth without changing the temperature itself. Therefore, the temperature at which the solid and liquid phases can coexist is identical for both solidifying and melting processes.

Understanding this equilibrium is crucial in thermodynamics and phase change processes, as it explains why a substance can transition between solid and liquid states at the same temperature under constant pressure conditions.