Internal energy represents the total energy contained within a system, encompassing both the kinetic and potential energies of its constituent particles. In contrast, enthalpy is defined as the sum of internal energy and the product of pressure and volume.

The internal energy of a system quantifies the energy associated with the motion and positional arrangements of its particles. As a state function, internal energy is determined solely by the current state of the system, independent of the pathway taken to reach that state. Changes in internal energy can occur through the addition or removal of heat or work.

Enthalpy, on the other hand, measures the heat energy that is either released or absorbed during a chemical reaction or physical transformation. Like internal energy, enthalpy is also a state function that depends only on the current state of the system. It is frequently utilized to describe the heat of a reaction, which is calculated as the difference between the enthalpy of the products and that of the reactants.

A key distinction between internal energy and enthalpy is that enthalpy accounts for the energy changes associated with pressure and volume fluctuations, whereas internal energy does not. This characteristic renders enthalpy a more practical measure for analyzing energy changes that occur during reactions or processes involving variations in pressure or volume.

In conclusion, while both internal energy and enthalpy serve as measures of a system’s energy, enthalpy encompasses the energy related to pressure and volume changes. This attribute makes enthalpy particularly useful for describing energy transformations during chemical reactions and physical processes.