Editing Enthalpy (section)

==History and etymology==
The term ''enthalpy'' was coined relatively late in the history of thermodynamics, in the early 20th century. [[Energy]] was introduced in a modern sense by [[Thomas Young (scientist)|Thomas Young]] in 1802, while [[entropy]] by [[Rudolf Clausius]] in 1865. ''Energy'' uses the root of the [[Ancient Greek language|Greek]] word {{lang|grc|{{math|ἔργον}}}} (''ergon''), meaning "work",<ref>{{LSJ|e)/rgon|ἔργον|shortref}}.</ref> to express the idea of capacity to perform work. ''Entropy'' uses the Greek word {{lang|grc|τροπή}} (''tropē'') meaning ''transformation'' or ''turning''.<ref>{{LSJ|troph/|τροπή|shortref}}.</ref> ''Enthalpy'' uses the root of the Greek word {{lang|grc|{{math|θάλπος}}}} (''thalpos'') "warmth, heat".<ref>{{LSJ|qa/lpos|θάλπος|shortref}}.</ref>

The term expresses the obsolete concept of ''heat content'',{{efn|group=note|
Howard (2002) quotes [[J. R. Partington]] in ''An Advanced Treatise on Physical Chemistry'' (1949) as saying that the function ''H'' was "usually called the heat content."
}} as {{math|d''H''}} refers to the amount of heat gained in a process at constant pressure only,<ref>
{{cite book
 |first1=Ignacio Jr. |last1=Tinoco
 |first2=Kenneth     |last2=Sauer
 |first3=James C.    |last3=Wang
 |date=1995
 |title=Physical Chemistry |edition=3rd
 |publisher=Prentice-Hall
 |isbn=978-0-13-186545-7
 |page=41
}}
</ref> but not in the general case when pressure is variable.<ref name=Laidler-Meiser-1982/> [[Josiah Willard Gibbs|J. W. Gibbs]] used the term "a heat function for constant pressure" for clarity.{{efn|group=note|
Volume&nbsp;I of Gibbs' ''Collected Works''<ref>{{harvp|Gibbs|1948}}</ref> does not contain the word ''enthalpy'', but uses the phrase ''"heat function for constant pressure"'' instead, for the same quantity.<ref>
{{Cite book
 |last1= Henderson |first1= Douglas
 |last2= Eyring    |first2= Henry
 |last3= Jost      |first3= Wilhelm
 |year= 1967
 |title= Physical Chemistry: An advanced treatise
 |publisher= Academic Press
 |page= 29
}}
</ref>
}}

Introduction of the concept of "heat content" {{mvar|H}} is associated with [[Benoît Paul Émile Clapeyron]] and [[Rudolf Clausius]] ([[Clausius–Clapeyron relation]], 1850).

The term ''enthalpy'' first appeared in print in 1909.<ref>
{{harvp|Dalton|1909|p=864, footnote&nbsp;(1)}}.<!-- {{cite journal
 |last=Dalton |first=J.P.
 |date=1909
 |title=Researches on the Joule–Kelvin-effect, especially at low temperatures. I.&nbsp;Calculations for hydrogen
 |journal=Koninklijke Akademie van Wetenschappen te Amsterdam [Proceedings of the Royal Academy of Sciences at Amsterdam, Section of Sciences]
 |volume=11 |issue=(part&nbsp;2) |pages=863–873 esp. see p.&nbsp;864, footnote&nbsp;(1).
 |url=https://www.biodiversitylibrary.org/item/49173#page/453/mode/1up
 |bibcode=1908KNAB...11..863D
}} -->
</ref> It is attributed to [[Heike Kamerlingh Onnes]], who most likely introduced it orally the year before, at the first meeting of the Institute of Refrigeration in Paris.<ref>{{harvp|Laidler|1995|p=110}}; {{harvp|van&nbsp;Ness|2003|p=486}}.<!--
{{cite book
 |last = Laidler |first = Keith |author-link = Keith J. Laidler
 |year = 1995
 |title = The World of Physical Chemistry
 |place = Oxford, UK
 |publisher = Oxford University Press
 |page = 110
}}
:
{{cite journal
 |last= van&nbsp;Ness |first= Hendrick C.
 |year= 2003
 |title=''H'' is for enthalpy
 |journal= Journal of Chemical Education
 |volume= 80 |issue= 6 |page = 486
 |bibcode= 2003JChEd..80..486V
 |doi= 10.1021/ed080p486.1 |doi-access= free
}}
-->
</ref> It gained currency only in the 1920s, notably with the ''[[enthalpy–entropy chart|Mollier Steam Tables and Diagrams]]'', published in 1927.

Until the 1920s, the symbol {{mvar|H}} was used, somewhat inconsistently, for "heat" in general. The definition of {{mvar|H}} as strictly limited to enthalpy or "heat content at constant pressure" was formally proposed by A. W. Porter in 1922.<ref>
{{cite journal |last=Porter |first=Alfred W. |date=1922 |title=The Generation and Utilisation of Cold. A General Discussion |url=https://babel.hathitrust.org/cgi/pt?id=njp.32101076787439;view=1up;seq=157 |journal=Transactions of the Faraday Society |volume=18 |pages=139–143 esp. p.&nbsp;140 |doi=10.1039/tf9221800139|url-access=subscription }}
</ref><ref name="Howard">
{{harvp|Howard|2002|p=697}}.<!-- {{Cite journal
 |last= Howard  |first= Irmgard K. 
 |year= 2002
 |title= ''H'' Is for Enthalpy, Thanks to Heike Kamerlingh Onnes and Alfred W. Porter
 |journal= Journal of Chemical Education
 |volume= 79 |issue= 6 |page = 697
 |bibcode = 2002JChEd..79..697H  |doi= 10.1021/ed079p697
}} -->
</ref>