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Enthalpy

Enthalpy is the total internal energy of any thermodynamic system added to the energy of the work done by the system on the atmosphere (pressure times volume). This additional energy typically results in heat energy being added to the system, and enthalpy translates almost directly into “put heat into it”.

The total enthalpy of a system cannot be directly measured, but its change can be. It is a thermodynamic potential and works best for processes involving near-constant pressure in which all energy input goes into internal energy and the work expanding the system. In the simplest systems, enthalpy difference is a measurement of the maximum amount of thermal energy you can derive from a given thermodynamic process within a system at a constant pressure. Because of this, it’s often called the heat content of a system.

Enthalpy for a given system tends to decrease to its minimum value, where it maintains equilibrium. In an exothermic reaction at constant pressure, the energy released in the reaction is equal to the system’s change in enthalpy; the reverse is true for an endothermic reaction.

Web Resources On Enthalpy

NASA: Enthalpy
First Law of Thermodynamics

Book Resources On Enthalpy

Handbook of Antioxidants: Bond Dissociation Energies, Rate Constants, Activation Energies, and Enthalpies of Reactions by Denisov et al.
Enthalpy Changes in Chemical Reactions/Hess's Law: Separate from Chemistry in the Laboratory by Postma et al.

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