Faasitasapaino

Faasitasapaino, or phase equilibrium, is the thermodynamic state in which two or more phases of a substance coexist in balance at a given temperature and pressure. In this state, the chemical potential of each component is the same in every coexisting phase, so there is no net transfer of matter between phases.

In a multi-component system, each phase has its own composition, but at equilibrium the chemical potentials of each component are equal across all phases. Phase boundaries are described by phase diagrams in which regions show which phases are stable at particular temperatures and pressures; lines of coexistence separate single-phase regions and end at points where more phases can coexist.

Examples include the solid-liquid boundary of water and ice at 0°C and 1 atmosphere, and the liquid-vapor boundary of water at its boiling point. The triple point is where solid, liquid, and vapor coexist, and the critical point marks where the distinction between liquid and vapor disappears.

Applications and relevance span materials science, metallurgy, crystallization, distillation, and polymer science. Phase equilibrium also occurs in natural processes such as cloud formation and ice melting. The Gibbs phase rule, F = C − P + 2, describes the degrees of freedom in a system with C components and P coexisting phases.

Note: phase equilibrium is distinct from chemical equilibrium, which concerns the balance of chemical reactions rather than the distribution of phases; phase equilibrium can occur without chemical reactions taking place.