Supersaturationa

Supersaturationa, commonly referred to as supersaturation, is a chemical state in which a solution contains more dissolved solute than is normally allowed to remain in equilibrium at a specified temperature (and pressure for gases). In a saturated solution, the rate of dissolution and precipitation are balanced; in a supersaturated solution, precipitation is suppressed by kinetic barriers, allowing the concentration to exceed equilibrium.

Formation: Supersaturation can be prepared by heating a solution to dissolve more solute, then cooling carefully; by evaporating solvent; or by rapid change of solvent composition or temperature that does not immediately trigger crystallization. The resulting metastable state can persist until a nucleation event occurs.

Stability and kinetics: Supersaturated solutions are metastable. They are sensitive to disturbances such as impurities, agitation, or seed crystals, which can initiate nucleation and rapid crystallization. Nucleation can be homogeneous (within the solution) or heterogeneous (on surfaces or impurities).

Applications: Supersaturation is exploited in crystallization processes in chemical engineering, pharmaceutical manufacturing for controlling drug crystallization, and in the culinary arts for sweets like rock candy. In meteorology, water vapor can become supersaturated, leading to cloud formation.

Measurement: The degree of saturation is the ratio of the actual solute concentration to the equilibrium solubility at the same temperature. A ratio greater than one indicates supersaturation. Practically, controlling temperature, solvent choice, and seeding are ways to manage supersaturation.

Examples: A classic demonstration is sodium acetate supersaturated solutions, which crystallize upon triggering a seed or disturbance. Sugar syrups can also be maintained in a supersaturated state to form crystals gradually.

Note on term: Supersaturationa appears to be a nonstandard spelling; the standard term is supersaturation.