Internal Energy of a Gas.
I. The internal energy of an ideal gas is purely kinetic.
II. For a real gas, internal energy includes both kinetic and potential energy contributions.
III. The internal energy of an ideal gas depends only on its temperature (U = f(T)).
IV. In an isothermal expansion of an ideal gas, the change in internal energy is zero.
V. The internal energy is a path function, depending on the process of heating.
