ABSTRACT
The concepts of energy conservation and entropy change are sufficient to explain the biological, biochemical, and physical phenomena in which we are interested. Physical chemists circumvent this problem by using a quantity called free energy. Free energy has the virtue that it can be described in terms of system parameters only, like the temperature, volume, and entropy of the system. The practical use of Gibbs' free energy requires that the temperature and pressure of the system remain constant. These are mathematical requirements, but they need not bother us because they are also biologically realistic. The free energy change in a reaction is obtained by subtracting the free energy of the initial state front that of the final state. Thus, a negative free energy change means that the free energy of the participants decreases during the process. Such exergonic processes are spontaneous because the entropy of the universe increases as system free energy decreases.
