Editing Water (section)

==== Phase transitions ====
At a pressure of one [[Standard atmosphere (unit)|atmosphere]] (atm), ice melts or water freezes (solidifies) at {{cvt|0|C|}} and water boils or vapor condenses at {{cvt|100|C|F}}. However, even below the boiling point, water can change to vapor at its surface by [[evaporation]] (vaporization throughout the liquid is known as [[boiling]]). Sublimation and deposition also occur on surfaces.<ref name=Belnay/> For example, [[frost]] is deposited on cold surfaces while [[snowflake]]s form by deposition on an aerosol particle or ice nucleus.<ref>{{cite web |last1=Wells |first1=Sarah |title=The Beauty and Science of Snowflakes |url=https://ssec.si.edu/stemvisions-blog/beauty-and-science-snowflakes |website=Smithsonian Science Education Center |access-date=25 March 2020 |language=en |date=21 January 2017 |archive-date=25 March 2020 |archive-url=https://web.archive.org/web/20200325185513/https://ssec.si.edu/stemvisions-blog/beauty-and-science-snowflakes |url-status=live }}</ref> In the process of [[freeze-drying]], a food is frozen and then stored at low pressure so the ice on its surface sublimates.<ref name=FreezeDrying>{{Cite book|title=Food processing technology: principles and practice|last=Fellows|first=Peter|date=2017|publisher=Woodhead Publishing/Elsevier Science|isbn=978-0-08-100523-1|edition=4th|location=Kent|pages=929–940|chapter=Freeze drying and freeze concentration|oclc=960758611}}</ref>

The melting and boiling points depend on pressure. A good approximation for the rate of change of the melting temperature with pressure is given by the [[Clausius–Clapeyron relation]]:

<math display="block"> \frac{d T}{d P} = \frac{T \left(v_\text{L}-v_\text{S}\right) }{L_\text{f}} </math>

where <math>v_\text{L}</math> and <math>v_\text{S}</math> are the [[molar volume]]s of the liquid and solid phases, and <math>L_\text{f}</math> is the molar [[latent heat]] of melting. In most substances, the volume increases when melting occurs, so the melting temperature increases with pressure. However, because ice is less dense than water, the melting temperature decreases.<ref name=Oliveira>{{cite book |last1=Oliveira |first1=Mário J. de |title=Equilibrium Thermodynamics |date=2017 |publisher=Springer |isbn=978-3-662-53207-2 |pages=120–124 |url=https://books.google.com/books?id=F8GRDgAAQBAJ&dq=denser+liquid+than+solid+phase+water+silicon+bismuth&pg=PA122 |access-date=26 March 2020 |language=en |archive-date=8 March 2021 |archive-url=https://web.archive.org/web/20210308003011/https://www.google.com/books/edition/Equilibrium_Thermodynamics/F8GRDgAAQBAJ?hl=en&gbpv=1&dq=denser+liquid+than+solid+phase+water+silicon+bismuth&pg=PA122&printsec=frontcover |url-status=live }}</ref> In glaciers, [[pressure melting point|pressure melting]] can occur under sufficiently thick volumes of ice, resulting in [[subglacial lake]]s.<ref>{{cite journal |last1=Siegert |first1=Martin J. |last2=Ellis-Evans |first2=J. Cynan |last3=Tranter |first3=Martyn |last4=Mayer |first4=Christoph |last5=Petit |first5=Jean-Robert |last6=Salamatin |first6=Andrey |last7=Priscu |first7=John C. |title=Physical, chemical and biological processes in Lake Vostok and other Antarctic subglacial lakes |journal=Nature |date=December 2001 |volume=414 |issue=6864 |pages=603–609 |doi=10.1038/414603a|pmid=11740551 |bibcode=2001Natur.414..603S |s2cid=4423510 }}</ref><ref>{{cite web |last1=Davies |first1=Bethan |title=Antarctic subglacial lakes |url=http://www.antarcticglaciers.org/glacier-processes/glacial-lakes/subglacial-lakes/ |website=AntarcticGlaciers |access-date=25 March 2020 |archive-date=3 October 2020 |archive-url=https://web.archive.org/web/20201003171536/http://www.antarcticglaciers.org/glacier-processes/glacial-lakes/subglacial-lakes/ |url-status=live }}</ref>

The Clausius-Clapeyron relation also applies to the boiling point, but with the liquid/gas transition the vapor phase has a much lower density than the liquid phase, so the boiling point increases with pressure.<ref>{{cite book |last1=Masterton |first1=William L. |last2=Hurley |first2=Cecile N. |title=Chemistry: principles and reactions |date=2008 |publisher=Cengage Learning |isbn=978-0-495-12671-3 |page=230 |edition=6th |url=https://books.google.com/books?id=teubNK-b2bsC&q=clapeyron%20equation%20boiling |access-date=3 April 2020 |archive-date=8 March 2021 |archive-url=https://web.archive.org/web/20210308080844/https://www.google.com/books/edition/Chemistry_Principles_and_Reactions/teubNK-b2bsC?hl=en&gbpv=1&bsq=clapeyron%20equation%20boiling |url-status=live }}</ref> Water can remain in a liquid state at high temperatures in the deep ocean or underground. For example, temperatures exceed {{convert|205|C}} in [[Old Faithful]], a geyser in [[Yellowstone National Park]].<ref>{{cite web |last1=Peaco |first1=Jim |title=Yellowstone Lesson Plan: How Yellowstone Geysers Erupt |location=Yellowstone National Park |publisher=U.S. National Park Service |url=https://www.nps.gov/yell/learn/education/classrooms/how-yellowstone-geysers-erupt.htm |access-date=5 April 2020 |language=en |archive-date=2 March 2020 |archive-url=https://web.archive.org/web/20200302093350/https://www.nps.gov/yell/learn/education/classrooms/how-yellowstone-geysers-erupt.htm |url-status=live }}</ref> In [[hydrothermal vent]]s, the temperature can exceed {{convert|400|C}}.<ref>{{cite news |last1=Brahic |first1=Catherine |title=Found: The hottest water on Earth |url=https://www.newscientist.com/article/dn14456-found-the-hottest-water-on-earth/ |access-date=5 April 2020 |work=New Scientist |archive-date=9 May 2020 |archive-url=https://web.archive.org/web/20200509103747/https://www.newscientist.com/article/dn14456-found-the-hottest-water-on-earth/ |url-status=live }}</ref>

At [[sea level]], the boiling point of water is {{convert|100|C}}. As atmospheric pressure decreases with altitude, the boiling point decreases by 1&nbsp;°C every 274&nbsp;meters. [[High-altitude cooking]] takes longer than sea-level cooking. For example, at {{convert|1524|m}}, cooking time must be increased by a fourth to achieve the desired result.<ref>{{cite web |last1=USDA Food Safety and Inspection Service |title=High Altitude Cooking and Food Safety |url=https://www.fsis.usda.gov/shared/PDF/High_Altitude_Cooking_and_Food_Safety.pdf |access-date=5 April 2020 |archive-date=20 January 2021 |archive-url=https://web.archive.org/web/20210120010850/https://www.fsis.usda.gov/shared/PDF/High_Altitude_Cooking_and_Food_Safety.pdf |url-status=dead }}</ref> Conversely, a [[pressure cooker]] can be used to decrease cooking times by raising the boiling temperature.<ref>{{cite web |title=Pressure Cooking – Food Science |url=https://www.exploratorium.edu/food/pressure-cooking |website=Exploratorium |language=en |date=26 September 2019 |access-date=21 April 2020 |archive-date=19 June 2020 |archive-url=https://web.archive.org/web/20200619044746/https://www.exploratorium.edu/food/pressure-cooking |url-status=live }}</ref> In a vacuum, water will boil at room temperature.<ref>{{cite news |last1=Allain |first1=Rhett |title=Yes, You Can Boil Water at Room Temperature. Here's How |url=https://www.wired.com/story/yes-you-can-boil-water-at-room-temperature-heres-how/ |access-date=5 April 2020 |magazine=Wired |date=12 September 2018 |language=en |archive-date=28 September 2020 |archive-url=https://web.archive.org/web/20200928044101/https://www.wired.com/story/yes-you-can-boil-water-at-room-temperature-heres-how/ |url-status=live }}</ref>