Clausius-Clapeyron Equation

Coexistence

Along a phase boundary the molar Gibbs free energies of two phases are equal. Differentiating this equality gives

$$\frac{dp}{dT}=\frac{\Delta s}{\Delta v} =\frac{L}{T\Delta v},$$

where $L$ is the latent heat per mole and $\Delta v$ is the molar volume change.

Interpretation

The equation tells how the transition pressure changes with temperature. It is especially useful for liquid-vapor coexistence and vapor pressure curves.