Other topics studied in thermal physics include : chemical potential, the quantum nature of an ideal gas, i . e . in terms of fermions and bosons, Bose Einstein condensation, Gibbs free energy, Helmholtz free energy, chemical equilibrium, phase equilibrium, the equipartition theorem, entropy at absolute zero, and transport processes as mean free path, viscosity, and conduction.
42.
Thus, in traditional use, the term free was attached to Gibbs free energy, i . e ., for systems at constant pressure and temperature, or to Helmholtz free energy, i . e ., for systems at constant volume and temperature, to mean available in the form of useful work . With reference to the Gibbs free energy, we add the qualification that it is the energy free for non-volume work.
43.
The maximum work is thus regarded as the diminution of the free, or available, energy of the system ( Gibbs free energy " G " at " T " = constant, " P " = constant or Helmholtz free energy " F " at " T " = constant, " V " = constant ), whilst the heat given out is usually a measure of the diminution of the total energy of the system ( Internal energy ).
