Enthalpy
Introduction
Enthalpy (from the Greek ἐνθάλπειν enthálpein "to add heat"; formed by ἐν- en- and θάλπειν thálpein "to heat") is a thermodynamic quantity, symbolized with the capital letter H, defined as "the flow of thermal energy in chemical processes carried out at constant pressure when the only work is pressure-volume",[1] that is, the amount of energy that a system exchanges with its environment. The term enthalpy was coined by the Dutch physicist Heike Kamerlingh Onnes, its use is documented in writing for the first time in 1909, in an article by J. P. Dalton "Researches on the Joule-Kelvin-effect, especially at low temperatures".[2].
In the history of thermodynamics, different terms have been used to denote what we know today as "enthalpy." It was originally thought that this word was created by Émile Clapeyron and Rudolf Clausius through the publication of the Clausius-Clapeyron relationship in The Mollier Steam Tables and Diagrams of 1927, but the first to define and use the term "enthalpy" was Onnes at the beginning of the century.[3].
In more specific words, it is a state function of thermodynamics where the variation allows expressing the amount of heat put into play during an isobaric transformation, that is, at constant pressure in a thermodynamic system, taking into account that every known object can be understood as a thermodynamic system. It is a transformation in the course of which energy can be received or provided (for example that used for mechanical work). In this sense, the enthalpy is numerically equal to the heat exchanged with the environment outside the system in question.
Within the International System of Units, enthalpy is usually measured in joules "Joule (unit)") which was originally introduced as the unit of work "Work (physics)").
The most typical case of enthalpy is the so-called thermodynamic enthalpy. From this it is worth distinguishing the Gibbs function, which corresponds to the free enthalpy, while the molar enthalpy is that which represents one mole of the constituent substance of the system.
thermodynamic enthalpy
Contenido
La entalpía (simbolizada generalmente como , también llamada , y calculada en julios "Julio (unidad)") en el sistema internacional de unidades o también en kcal o, si no, dentro del sistema anglosajón: BTU), es una función de estado extensiva, que se define como la transformada de Legendre de la energía interna con respecto del volumen.