Supercritical Liquid
Definition and meaning of Supercritical Liquid in chemistry.
A supercritical liquid is a fluid substance at or above its critical temperature and critical pressure, where the distinction between liquid and gas phases ceases to exist.
In more detail
Above the critical point of any substance, the phase boundary separating liquid and gas disappears, forming a supercritical fluid. This state exhibits hybrid properties: liquid-like density and solvating power, combined with gas-like diffusivity, viscosity, and compressibility. Though "supercritical liquid" is used colloquially, "supercritical fluid" is the precise scientific term. Supercritical fluids are widely employed in extraction, cleaning, and green chemistry applications because they avoid traditional phase transitions.
Key facts
| Field | Physical Chemistry |
|---|---|
| Definition | Substance above its critical temperature and pressure |
| Key properties | High density (liquid-like), low viscosity (gas-like), high diffusivity |
| Example compound | CO2 |
Supercritical carbon dioxide (above 31.1°C and 73.8 bar) is used industrially to extract caffeine from coffee beans and to clean precision electronic components without harsh chemical solvents.
Frequently asked questions
Why is 'supercritical liquid' not the standard term?
Above the critical point, neither a distinct liquid nor gas phase exists. The scientifically precise term is 'supercritical fluid,' as the substance is neither truly liquid nor gas.
What makes supercritical fluids industrially valuable?
They combine liquid-like solvency and density with gas-like transport properties, enabling efficient extraction and processing while serving as environmentally benign alternatives to volatile organic solvents.