Phase Transitions

A phase transition is a transformation from one phase to another at a specific transition temperature under given pressure conditions and is spontaneous only under these conditions.

Phase transitions are governed by temperature and pressure changes, which alter the balance between intermolecular forces and molecular motion or spacing.

During a phase transition, both phases coexist, and the substance's temperature remains constant. So, phase transitions are isothermal processes.

Since the chemical potentials of multiple phases of the same component are equal at equilibrium, the Gibbs free energy for an isothermal phase transition equals zero.

By substituting this into the Gibbs free energy equation, the entropy change for the phase transition can be expressed as the ratio of the enthalpy of phase change to the transition temperature.

In addition, the amount of heat absorbed or released during a phase transition is the product of the mass of the component and the enthalpy of the phase change.

The heat exchange can also be expressed in terms of moles by replacing the mass with the number of moles.