Editing Water (section)

==== Triple and critical points ====
[[File:Phase diagram of water.svg|thumb|Phase diagram of water]]
On a pressure/temperature [[phase diagram]] (see figure), there are curves separating solid from vapor, vapor from liquid, and liquid from solid. These meet at a single point called the [[triple point]], where all three phases can coexist. The triple point is at a temperature of {{convert|273.16|K|C F}} and a pressure of {{convert|611.657|Pa|atm psi|sigfig=3}};<ref>{{cite journal |last1=Murphy |first1=D. M. |last2=Koop |first2=T. |title=Review of the vapour pressures of ice and supercooled water for atmospheric applications |journal=Quarterly Journal of the Royal Meteorological Society |date=1 April 2005 |volume=131 |issue=608 |page=1540 |doi=10.1256/qj.04.94 |bibcode=2005QJRMS.131.1539M |s2cid=122365938 |url=https://zenodo.org/record/1236243 |access-date=31 August 2020 |archive-date=18 August 2020 |archive-url=https://web.archive.org/web/20200818105335/https://zenodo.org/record/1236243 |url-status=live |doi-access=free }}</ref> it is the lowest pressure at which liquid water can exist. [[2019 revision of the SI|Until 2019]], the triple point was used to define the [[Kelvin|Kelvin temperature scale]].<ref>{{cite book |author=International Bureau of Weights and Measures |author-link=International Bureau of Weights and Measures |date=2006 |url=http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf |url-status=live |archive-url=https://web.archive.org/web/20170814094625/http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf |archive-date=14 August 2017 |title=The International System of Units (SI) |edition=8th |isbn=92-822-2213-6 |page=114|publisher=Bureau International des Poids et Mesures }}</ref><ref name=Brochure9_2019>{{cite web |title = 9th edition of the SI Brochure |publisher = BIPM |url = https://www.bipm.org/en/publications/si-brochure/ |date = 2019 |access-date = 20 May 2019 |df = dmy-all |archive-date = 19 April 2021 |archive-url = https://web.archive.org/web/20210419211921/https://www.bipm.org/en/publications/si-brochure |url-status = live }}</ref>

The water/vapor phase curve terminates at {{convert|647.096|K|C F}} and {{convert|22.064|MPa|psi atm}}.<ref name=IAPWS95>{{cite journal |last1=Wagner |first1=W. |last2=Pruß |first2=A. |title=The IAPWS Formulation 1995 for the Thermodynamic Properties of Ordinary Water Substance for General and Scientific Use |journal=Journal of Physical and Chemical Reference Data |date=June 2002 |volume=31 |issue=2 |page=398 |doi=10.1063/1.1461829}}</ref> This is known as the [[critical point (thermodynamics)|critical point]]. At higher temperatures and pressures the liquid and vapor phases form a continuous phase called a [[supercritical fluid]]. It can be gradually compressed or expanded between gas-like and liquid-like densities; its properties (which are quite different from those of ambient water) are sensitive to density. For example, for suitable pressures and temperatures it can [[miscibility|mix freely]] with [[Nonpolar molecule|nonpolar compounds]], including most [[organic compound]]s. This makes it useful in a variety of applications including high-temperature [[electrochemistry]] and as an ecologically benign solvent or [[catalysis|catalyst]] in chemical reactions involving organic compounds. In Earth's mantle, it acts as a solvent during mineral formation, dissolution and deposition.<ref>{{cite journal |last1=Weingärtner |first1=Hermann |last2=Franck |first2=Ernst Ulrich |title=Supercritical Water as a Solvent |journal=Angewandte Chemie International Edition |date=29 April 2005 |volume=44 |issue=18 |pages=2672–2692 |doi=10.1002/anie.200462468|pmid=15827975 }}</ref><ref>{{cite journal |last1=Adschiri |first1=Tadafumi |last2=Lee |first2=Youn-Woo |last3=Goto |first3=Motonobu |last4=Takami |first4=Seiichi |title=Green materials synthesis with supercritical water |journal=Green Chemistry |date=2011 |volume=13 |issue=6 |pages=1380 |doi=10.1039/c1gc15158d}}</ref>