enthalpy

enthalpy
/en"thal pee, en thal"-/, n., pl. enthalpies. Thermodynamics.
a quantity associated with a thermodynamic system, expressed as the internal energy of a system plus the product of the pressure and volume of the system, having the property that during an isobaric process, the change in the quantity is equal to the heat transferred during the process. Symbol: H Also called heat content, total heat.
[1925-30; < Gk enthálp(ein) to warm in (en- EN-2 + thálpein to warm) + -Y3]

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Sum of the internal energy E and the product of the pressure P and volume V of a thermodynamic system (see thermodynamics).

So, enthalpy H = E + PV. Its value is determined by the temperature, pressure, and composition of the system at any given time. According to the law of conservation of energy (see conservation law), the change in internal energy is equal to the heat transferred to the system minus the work done by the system. If the only work done is a change of volume at constant pressure, the enthalpy change is exactly equal to the heat transferred to the system.

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      the sum of the internal energy and the product of the pressure and volume of a thermodynamic system. Enthalpy is an energy-like property or state function—it has the dimensions of energy, and its value is determined entirely by the temperature, pressure, and composition of the system and not by its history. In symbols, the enthalpy, H, equals the sum of the internal energy, E, and the product of the pressure, P, and volume, V, of the system: H = E + PV.

      According to the law of energy conservation (energy, conservation of), the change in internal energy is equal to the heat transferred to, less the work done by, the system. If the only work done is a change of volume at constant pressure, the enthalpy change is exactly equal to the heat transferred to the system. As with other energy functions, it is neither convenient nor necessary to determine absolute values of enthalpy. For each substance, the zero-enthalpy state can be some convenient reference state.

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Universalium. 2010.

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