Thermodynamic potential energies for macroscopic systems have been coined, analogous to mechanical potentials for microscopic systems, whose changes often amount to the best possible work a system or process can perform under specific constraints.Conventional examples of thermodynamic energies are the internal energy E, Helmholtz free energy F, Gibbs free energy G, and enthalpy H.In the thermodynamic limit, thermodynamic energies are state functions with the dimension of energy, which can be determined by observation on the equilibrium state of the system, independent of its history or the process producing the state.For ease of discussion, we will focus our attention on one-component simple system, which should not be considered as a fundamental limitation on the generality of our treatment.