Water/Freezing point: Difference between revisions
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imported>Chris Day (revert to last version that mentioned it was not measureable) |
imported>Milton Beychok m (Expanded references 7 and 8 to be more informative rather than merely providing urls) |
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<includeonly>Not | <includeonly>Not measurable*</includeonly> | ||
<noinclude>Not measurable</noinclude> | |||
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Note: The freezing point of "pure" water is not measurable,<ref>For more information on why the freezing point of pure water is not measurable see:[http://www.iapws.org/relguide/Ice-Rev2009.pdf 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</ref><ref>For more information on the [[Colligative properties|colligative property]] of freezing point depression of water by adding of a solvent (such as a salt) see:[http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/meltpt.html Freezing Point Depression in Solutions] Rod Nave, Department of Physics and Astronomy, [[Georgia State University]]</ref> whereas the melting point is. This is because pure water does not freeze without help of a solid crystallization kernel.<ref>[http://www.newton.dep.anl.gov/askasci/gen01/gen01672.htm Supercooled Water Demonstration,10/16/2004] from the website of the [[Argonne National Laboratory]]</ref> 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<ref>[http://polymer.bu.edu/hes/articles/ms98.pdf The relationship between liquid, supercooled and glassy water, Osamu Mishima & H. Eugene Stanley] ''Nature'', vol 396, 26 November 1998</ref>) and (231 K=-43.9°C<ref>[http://polymer.bu.edu/hes/articles/ds03.pdf Supercooled and Glassy Water, Pablo G. Debenedetti and H. Eugene Stanley] ''Physics Today'', vol 40, June 2003</ref>). | |||
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<ref>[http://www.bipm.org/en/si/si_brochure/chapter2/2-1/kelvin.html Unit of thermodynamic temperature (kelvin)] From the website of the [[Bureau International des Poids et Mesures]] (BIPM)</ref><ref name=NIST>[http://physics.nist.gov/cuu/Units/kelvin.html Unit of thermodynamic temperature (kelvin)] From the website of the [[National Institute of Standards and Technology]] (NIST)</ref> as the fraction 1/273.16 of waters triple point. Formerly (until 1954<ref name=NIST/> the definition developed by [[Anders Celsius]] had fixed the 0°C point at the "freezing point" of water.<ref>[http://www.energyquest.ca.gov/scientists/celsius.html Anders Celsius] From the website of the [[California Energy Commission]]</ref> 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.{{Reflist}}</noinclude> | |||
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Latest revision as of 18:12, 28 July 2010
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