Free Energy and Its Significance

Thermodynamics is a powerful tool for the study of chemical reactions and is intimately related to the atomic and molecular description of the species participating in these reactions. The transformation of energy involved in the reactions depends on the thermodynamic conditions of the reaction, and can be expressed in terms of various thermodynamic functions. One such function is the Gibbs free energy [1-4], expressed by Eq. (1)  

The concept described above will now be elaborated upon by examining the effect of expansion for a reversible process. Defining H = U + PV, where U refers to internal energy, T to temperature and P to pressure, and substituting it in Eq. (1) results in  

The work done by the system, -Sw, consists of the work of expansion, Pd V, and useful work, —Sw. Hence 

the decrease in free energy for a reaction is the maximum work that could be obtained at constant temperature and pressure. Therefore, reactions exhibiting a negative AG are those that can be harnessed to do work. 

AG for a given reaction can be positive, negative, or zero. If AG = 0. the system is in equilibrium. If AG is negative, the reaction can proceed spontaneously as written, and if it is positive, the reaction will not proceed unless driven by an external force, such as the application of voltage during electrolysis. 

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