Water/Freezing point
Not measurable
Note: The freezing point of "pure" water is not measurable,[1][2] whereas the melting point is. This is because pure water does not freeze without help of a solid crystallization kernel.[3] Very cold (metastable) pure liquid water can be obtained by "supercooling" pure water. Pure liquid water has been reported to be possible down to various extremely low temperatures: (-38°C to -45°C[4]) and (231 K=-43.9°C[5]).
The standard unit of thermodynamic temperature, currently defined in the SI system as K (Kelvin), selects as the fundamental fixed point the triple point of water. One Kelvin, and therefore 1°C (Celsius), is specified by multiple standards bodies[6][7] as the fraction 1/273.16 of waters triple point. Formerly (until 1954[7] the definition developed by Anders Celsius had fixed the 0°C point at the "freezing point" of water.[8] It is now generally accepted that while the phase transition from solid to liquid water occurs at a predictable temperature (namely 0°C), the transition from liquid to solid water does not. This is because the actual "Freezing" is dependent upon the previously mentioned nucleation as well as the temperature.
- ↑ For more information on why the freezing point of pure water is not measurable see:Revised Release on the Equation of State 2006 for H2O Ice Ih The International Association for the Properties of Water and Steam, The Netherlands, September 2009
- ↑ For more information on the colligative property of freezing point depression of water by adding of a solvent (such as a salt) see:Freezing Point Depression in Solutions Rod Nave, Department of Physics and Astronomy, Georgia State University
- ↑ Supercooled Water Demonstration,10/16/2004 from the website of the Argonne National Laboratory
- ↑ The relationship between liquid, supercooled and glassy water, Osamu Mishima & H. Eugene Stanley Nature, vol 396, 26 November 1998
- ↑ Supercooled and Glassy Water, Pablo G. Debenedetti and H. Eugene Stanley Physics Today, vol 40, June 2003
- ↑ Unit of thermodynamic temperature (kelvin) From the website of the Bureau International des Poids et Mesures (BIPM)
- ↑ 7.0 7.1 Unit of thermodynamic temperature (kelvin) From the website of the National Institute of Standards and Technology (NIST)
- ↑ Anders Celsius From the website of the California Energy Commission