 Clausius–Clapeyron relation

Along a first-order coexistence curve,At a critical point the two phases merge, their entropy jump vanishes, and the latent heat tends to zero.

The Clausius–Clapeyron relation is a fundamental equation in thermodynamics that describes the relationship between the pressure and temperature of a phase transition, particularly between the liquid and vapor phases of a substance. It is particularly useful for understanding vaporization and sublimation processes.