critical point temperature
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What is the Critical Temperature?
The critical temperature (Tc, or critical point temperature) is the temperature above which
a gas cannot be made to liquefy, no matter how great the pressure applied.
The corresponding critical pressure (Pc) is the minimum pressure that must
be applied to bring about liquefaction at the critical temperature.
The Gas-Liquid Critical Point
The critical point temperature or critical state temperature of any material
is that temperature above which there is no distinct existence of liquid and gas
phases. The phase properties of the gas and liquid become the same as the
critical point temperature approaches. Only one phase exists at this point which
is also known as a homogeneous supercritical fluid when the temperature is
equal to the critical point temperature.
The heat of vaporization
becomes zero at this critical point temperature. No further increase in pressure
can form a liquid but solidification may occur if the
pressure is increased sufficiently. The critical point temperature is a property of the substance.
For water, the
critical point occurs at around 647 K (374 °C or 705 °F) and 22.064 MPa (3200
PSIA or 218 atm).
Other Related Properties
The critical molar volume
represents the volume of one mole of substance at the critical temperature and
The liquid-liquid critical point of a solution is the point at which it gets separated
into two different liquids of different densities. This is the point at which any
change in temperature or pressure will separate the mixture into two distinct
liquid phases. Such points
are also known as the critical solution temperature.
The upper critical solution temperature (UCST) is the warmest
point at which cooling will cause phase separation, and the lower
critical solution temperature (LCST) is the coolest
point at which heating will cause phase separation.
Divergences at Critical Point
Every fluid has a different critical point. The end of the vapour
pressure is marked by the critical point on the pressure-temperature
curve; this phase transition is different from the phenomenon of boiling
that occurs along the vapor pressure curve. There are other anomalies
near the critical point as the
isothermal compressibility and heat capacity approach
infinity as the fluid approaches Tc.
The critical points of ferromagnetic materials such as iron are known as the Curie Point,
where, again, a number of anomalies occur including singularities in heat capacity and divergent magnetic