Supersaturation

Supersaturation is a metastable state in which a solution contains more dissolved solute than its equilibrium solubility permits. It persists until crystallization or another process reduces the excess.

Solubility: The maximum amount of a substance that can dissolve in a specified solvent under stated conditions. Supersaturation means the dissolved concentration exceeds this equilibrium limit.
Phase equilibrium: A condition in which phases coexist without net transfer of matter between them. Solubility defines the equilibrium boundary that supersaturation crosses.
Crystallization: The formation of solid crystals from a solution, melt, or vapor. It is the principal process used to consume excess dissolved solute.
Unsaturated solution: A solution containing less dissolved solute than its equilibrium solubility permits. Unlike supersaturation, it can dissolve additional solute without precipitation.
Chemical potential: A thermodynamic quantity measuring how a system’s free energy changes when particles are added. The chemical-potential difference drives the system toward precipitation or crystallization.
Solute: A substance dissolved in a solvent to form a solution. Its concentration is the quantity that exceeds the equilibrium limit.
Fractional crystallization: A separation method that crystallizes components in sequence according to their different solubilities. Carefully controlled supersaturation allows selected compounds to crystallize first.
Saturated solution: A solution containing the equilibrium maximum of dissolved solute under specified conditions. It marks the equilibrium threshold that supersaturation exceeds.
Nucleation: The formation of stable initial clusters from which a new phase can grow. Nucleation often determines how long excess solute remains dissolved.
Solvent: The component of a solution that dissolves another substance. Solvent identity and conditions determine how much solute can remain dissolved.

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