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ENTHALPY

Enthalpy, or, thermal content, of a system is designated by the symbol H and it is defined as H = E + PV, where
E is the internal energy of the system,
P is pressure,
V is volume.

As a rule, absolute values of enthalpy and internal energy are not known, so, this definition is more often used in terms of increments: ΔH = ΔE + Δ(PV).