Topic overview

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At a phase boundary, coexisting phases have equal chemical potentials, and the Gibbs energy change for the transition is zero. Enthalpy and entropy changes describe first-order transitions, while the Clapeyron equation relates the slope of a phase boundary to those changes and the volume difference. For vaporization, the Clausius–Clapeyron form links vapor pressure with temperature. The topic also distinguishes triple and critical points, compares first- and second-order transitions, and uses Gibbs energy curves to identify stable phases. Metastability and solid-solution equilibria extend the discussion to situations where kinetic barriers or mixing affect phase behavior.