Free energy endergonic processes

If AG is equal to 0, the process is at equilibrium, and there is no net flow either in the forward or reverse direction. When AG = 0, A.S = H/T, and the enthalpic and entropic changes are exactly balanced. Any process with a nonzero AG proceeds spontaneously to a final state of lower free energy. If AG is negative, the process proceeds spontaneously in the direction written. If AG is positive, the reaction or process proceeds spontaneously in the reverse direction. (The sign and value of AG do not allow us to determine how fast the process will go.) If the process has a negative AG, it is said to be exergonic, whereas processes with positive AG values are endergonic. 

These resonance stabilization energies of free radicals can be quite large, e.g. 50 kj mol 1 for benzyl-, and 70kjmol 1 for methyl-Np. These must be included in the overall energy balance of the reaction, and can make all the difference between a fast, highly exergonic process, and an endergonic process which in practice does no take place at all. 

There is a sufficient decrease in the free energy of glucose to couple the process of glucose degradation with the substrate-level phosphorylation of two molecules of ADP, which is an endergonic reaction ... 

In order to successfully compete with BET the cleavage reactions must have small activation barriers. A prerequisite for small activation energies is a small positive (for endergonic processes) or negative free energy (AGm). The free energy of radical ion cleavage (mesolysis) may be conveniently estimated from simple thermodynamic cycles [74, 75] (Scheme 2). 

The change in free energy is negative when A5 univ is positive, which reflects a spontaneous reaction said to be exergonic (Figure 4.4). If the AG is positive, the process is said to be endergonic (nonspontaneous). When the AG is zero, the process is at equilibrium. As with other thermodynamic functions, AG provides no information about reaction rates. Reaction rates depend on the precise mechanism by which a process occurs and are dealt with under the study of kinetics (Chapter 6). 

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