Enthalpic

Enthalpic is an adjective used in thermodynamics to describe properties or processes related to enthalpy, a thermodynamic state function that characterizes the heat content of a system. Enthalpy is denoted H and is defined for a simple compressible system as H = U + pV, where U is internal energy, p is pressure, and V is volume.

One practical aspect of enthalpy is the relation between heat and enthalpy change: for a process carried out at constant pressure, the heat added to or removed from the system equals the change in enthalpy, ΔH = q_p.

Enthalpy depends on temperature and composition. The molar enthalpy h is H per mole. The temperature derivative of enthalpy at constant pressure defines the molar heat capacity, Cp = (∂H/∂T)_p. Common enthalpy terms include the standard enthalpy of formation, ΔHf°, the standard enthalpy of reaction, ΔHr°, and the enthalpies of phase transitions such as fusion (ΔHfus) and vaporization (ΔHvap). The standard enthalpy of combustion ΔHc° quantifies heat released during burning of a substance with oxygen.

Calculations use enthalpy values from tables; H is a state function, enabling path-independent calculations. Units: H and ΔH are measured in joules; molar enthalpy in joules per mole. Cp has units J/(mol K).

Enthalpic properties are distinct from entropy or Gibbs energy but are related through thermodynamic relations. The term enthalpic simply refers to properties, changes, or processes involving enthalpy.