How is enthalpy defined?

Enthalpy is a thermodynamic state function defined as the sum of the internal energy of a system and the product of its pressure and volume. It is represented by the equation H = U + pV, where H is the enthalpy, U is the internal energy, p is the pressure, and V is the volume.

This definition is significant because it allows for the assessment of energy changes that occur at constant pressure, which is a common condition for many processes in chemistry and engineering. By incorporating pressure and volume, enthalpy provides a more complete picture of the heat content of a system, especially during reactions that take place in an open system.

Considering various thermodynamic processes, this relationship is crucial when dealing with changes in state, such as in calorimetry, where heat transfer occurs at constant pressure. Hence, the formulation illustrates not just the internal energy but also the work done by the system when it expands or contracts, making it an essential term in thermodynamics, particularly in the context of chemical reactions and phase changes.