The textbook I am currently reading (An Introduction to Thermal Physics by Schroeder) states that the total thermal energy of a system is given by:
where n is the total number of molecules and f is the degrees of freedom of the molecules.
Correct me if I'm wrong, but the thermal energy of a system consists of both the kinetic energies of molecules as well as their potential energies due to the intermolecular forces associated with phase of the molecules. And as far as I know, the phase of the molecules (and hence the potential energies of the molecules) depends on both temperature AND the pressure of the system. This leads me to question: why there isn't a term in this equation that contains the pressure of the system? Does this equation assume that the system is an ideal gas which then there would be no potential energies involved?