 Helmholtz proposed the notion of a “free energy” to account for cases involving heat and entropy. The Helmholtz free energy is defined as F ⇔ E − TS, where E is energy, T is temperature, and S is entropy. The free energy equation yields a quantity, F, that is independent of heat and entropy. Many equations involving F and not T or S are fully reversible, and so Helmholtz’s work allowed for the application of the Hamiltonian to many chemical processes. Hence while “Helmholtz was neither the sole nor the most important contributor” to theoretical chemistry, “his thermodynamic theory of 1882–1883 was the pioneering work on which much of the new theoretical chemistry rested” (Kragh 1993, 406).