supersaturated

Supersaturated is a term used in chemistry to describe a solution that contains more dissolved solute than the equilibrium solubility at a given temperature and pressure. In this state, the solution is not at equilibrium; the excess solute is held in solution by kinetic barriers that prevent immediate crystallization.

Supersaturation is typically achieved by dissolving solute at a higher temperature and then cooling the solution slowly, or by evaporating a solvent to concentrate the solution beyond its normal solubility. It can also occur in gas systems where vapor concentration exceeds equilibrium, such as in atmospheric supersaturation of water vapor. Supersaturated solutions are metastable: they can persist, but they are sensitive to disturbance. A seed crystal, a shock, or a surface can trigger crystallization, causing rapid precipitation of the solute until the system returns to equilibrium.

Common demonstrations and applications include a supersaturated sodium acetate solution that crystallizes when seeded, producing a sudden solidification and heat release. In pharmaceutical and chemical engineering, supersaturation is exploited to enhance dissolution and crystallization control, such as in drug formulation where amorphous forms or solvent/anti-solvent methods create transient supersaturation to improve bioavailability. In nature, supersaturation of water vapor is a prerequisite for cloud formation and precipitation processes.