ABSTRACT
When the process taking place in the system is spontaneous, in principle it can be harnessed to deliver work to the surroundings. Conversely, when the process is non-spontaneous, we must do work on the system in order to make the process occur. According to the Second Law of Thermodynamics, the process taking place in our system is spontaneous if
6Suniv = 6Ssyst + 6Ssurr > 0 . . . [1]
Calculating 6Suniv is cumbersome because, although we usually are concerned primarily with what is taking place in the system-–where the process of interest occurs-–we also must calculate 6Ssurr to find out if our process is spontaneous. For this purpose a more useful function than the entropy is the Gibbs Free Energy G, defined as
G > H – TS Gibbs Free Energy . . . [2]
In Eqn [2] H is the enthalpy of the system, T is its temperature, and S is its entropy. G is a state function because all its components are state functions. Furthermore, G is a property of the system, not of the surroundings. The Gibbs Free Energy is named after J. Willard Gibbs, a famous nineteenth century American thermodynamicist who is considered to be the “father” of chemical thermodynamics.
