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Critical properties vary from material to material, just as is the case for the Melting Point and Boiling Point . Critical properties for many pure substances are readily available in the literature. Obtaining critical properties for mixtures is somewhat more problematic.

For pure substances, there is an Inflection Point in the critical Isotherm on a PV diagram. This means that at the critical point:

:\left( rac{\partial P}{\partial V} ight)_T = \left( rac{\partial^2P}{\partial V^2} ight)_T = 0

This relation can be used to evaluate two parameters for an equation of state in terms of the critical properties.

Sometimes a set of reduced properties are defined in terms of the critical properties, ie.:

:T_r = T/T_c

:P_r = P/P_c

:V_r = V/V_c

The ''principle of corresponding states'' indicates that substances at equal reduced pressures and temperatures have equal reduced volumes. This relationship is approximately true for many substances, but becomes increasingly inaccurate for large values of Pr

Two Immiscible liquids, such as oil and water, will also have a critical temperature and pressure at which the two phases will become consolute.


CRITICAL TEMPERATURE OF SELECTED ELEMENTS
























Element'''Critical temperature (°C)'''
Argon -122.29
Arsenic 1400
Bromine 315
Chlorine 143.8
Fluorine -128.85
Helium -267.96
Hydrogen -240.17
Iodine 546
Krypton -63.7
Mercury 1477
Neon -228.75
Nitrogen -146.9
Oxygen -118.57
Phosphorus 721
Radon 105
Selenium 1493
Sulfur 1041
Xenon 16.58



CRITICAL TEMPERATURE OF SELECTED MOLECULE S
















Compound'''Critical temperature (°C)''''''Critical pressure (atm)'''
Ammonia (NH3)132115
Carbon Dioxide (CO2)31.277
Carbon Monoxide (CO)-14135.9
Ethanol (C2H6O)21665
Methane (CH4)-8245.8
Propane (C3H8)9742
Sulfur Dioxide (SO2)15777.8
Water (H2O)374217.8



IN SUPERCONDUCTIVITY

In superconductivity applications, critical temperature refers to the temperature below which a given material becomes superconductive.


IN CONSTRUCTION AND PASSIVE FIRE PROTECTION

Critical Temperature refers to the temperature above which structural Steel loses its strength and is no longer fully capable of loadbearing support. Maintaining structural and important process steel building components below this critical temperature, which varies from Country to Country but is generally between 500 and 560°C, is an important function of Passive Fire Protection .


SEE ALSO




LITERATURE