entalpia

Entalpia, also known as enthalpy, is a thermodynamic property that represents the heat content of a system at constant pressure. It is a state function, meaning its value depends only on the current state of the system, not on how that state was reached. The quantity is denoted by H and is defined by the relation H = U + pV, where U is the internal energy, p is pressure, and V is volume.

The differential form of enthalpy is dH = dU + p dV + V dp. For a simple compressible system undergoing only pressure-volume work, dU = δQ − p dV, which leads to dH = δQ + V dp. Consequently, at constant pressure (dp = 0), the infinitesimal enthalpy change equals the heat added to the system: δQ_p = dH. Thus, the enthalpy change ΔH for a process at constant pressure corresponds to the heat exchanged with the surroundings.

Enthalpy is helpful because it isolates heat transfer under constant pressure, a common condition in chemistry and engineering. For ideal gases, enthalpy is a function of temperature only, with cp = dH/dT at constant pressure. In chemistry, standard enthalpies of formation, reaction enthalpies, and calorimetry measurements rely on ΔH values. Enthalpy changes play a central role in predicting reaction spontaneity under varying conditions and in designing energy-efficient processes.