Most chemical processes (laboratory and industrial) occur in liquid phases used as reaction or separation media. Processes in the liquid state benefit from a comparatively fast mass and heat transfer, low viscosity, and high particle density. Dense states, however, can also be generated in compressed gases. At low temperature, if a gas is compressed to high density, it will condense into a liquid. Above a certain temperature, known as the critical temperature, any gas can be compressed gradually to a liquidlike density without undergoing such a transition. The resulting dense phase is called a supercritical fluid.