# Heat content

In thermodynamics, heat content, or rarely free heat content or total heat, is a name used to describe the characteristic function: [1]

$U + PV \,$

which is the sum of the internal energy U of a body or system plus the energy associated with pressure volume work PV.

Etymology
The term “heat content”, or heat-content, in thermodynamics, is sometimes said to be attributed to Gibbs, but he does not seem to have employed this term, at least according to key word search of his 1876 Equilibrium. The exact person to have first used this term needs to be tracked down.

Whatever the case, the term seems to have come into use in the second half of the 19th century.

In 1909, term “heat content” by the term “enthalpy”, a term introduced by the Dutch physicist Heike Kamerlingh-Onnes who assigned the symbol H to the function and the name enthalpy, from the Greek εν (en) ‘in’ and θαλπος (thalpos) ‘to heat’, which combined define the word enthalpos, to warm within. [2]

References
1. (a) Kortum, Gustav and Bockris, John O’M. (1951). Textbook of Electrochemistry (heat content, 26+ pgs). Elsevier.
(b) Laidler, Keith J. (1993). The World of Physical Chemistry (pg. 110). Oxford University Press.