supercools

Supercools is a term used to describe a phenomenon in physics where a liquid is cooled below its freezing point without solidifying. This state is called a metastable state because the liquid is not in its most stable form. The molecules within the supercooled liquid are still moving freely, as they would in a liquid, but the temperature is low enough that the formation of a solid crystal lattice is thermodynamically favorable.

For a liquid to supercool, it must be free of nucleation sites. Nucleation sites are impurities or imperfections on the surface of a container or within the liquid itself that provide a starting point for crystal formation. Without these sites, the molecules lack the necessary structure to begin organizing into a solid. When a nucleation site is introduced, either by disturbing the liquid, adding an impurity, or sometimes spontaneously due to random molecular motion, the supercooled liquid can rapidly solidify. This process is often exothermic, releasing heat as the liquid transforms into a solid.

Water is a commonly cited example of a liquid that can be supercooled. Tap water, due to dissolved minerals and imperfections in its container, typically freezes at or near its normal freezing point of 0 degrees Celsius (32 degrees Fahrenheit). However, highly purified water in a very clean container can be cooled significantly below this temperature without freezing. The rapid solidification of supercooled water is often observed when a supercooled liquid is shaken or when an object is dropped into it, causing instantaneous ice formation. This phenomenon has practical applications, such as in the production of artificial snow and in some cooling technologies.