Overmettet

Overmettet is a term used in several Scandinavian languages, especially Danish and Norwegian, to describe a solution that contains more dissolved solute than its solubility limit at a particular temperature. In English, the corresponding concept is oversaturation or supersaturation. In Swedish, the term is övermättad, but the meaning is the same: a metastable state in which a solution holds more solute than allowed by the equilibrium solubility. An overmettet solution is thermodynamically unstable and can remain in a metastable state until a perturbation—such as a seed crystal, an impurity, agitation, or a temperature change—induces nucleation and crystal growth.

Preparation commonly involves dissolving a solute at high temperature to maximize solubility, then cooling the solution slowly without allowing crystals to form. If the cooling occurs without triggering nucleation, the concentration remains higher than the equilibrium amount for the cooler temperature, creating an overmettet, or supersaturated, state. This state is exploited in crystallization processes to produce high-quality crystals and in various laboratory demonstrations.

Common examples include supersaturated sugar solutions used to make rock candy, where slow cooling allows sugar to remain dissolved beyond its normal solubility; similar approaches are used in pharmaceutical crystallization and materials science. In meteorology, supersaturation refers to air containing more water vapor than its capacity at a given temperature, which can lead to condensation and cloud formation when nucleation sites are present.

Characteristics: overmettet solutions are sensitive to disturbance and can precipitate rapidly once nucleation begins. Solubility curves and temperature control are essential to managing the state.