Indirect Metricization of Chemical Potential

Let us recapitulate The stronger the drive of a substance B to transform, here in particular the drive of the substance to decompose into the elements (in their standard state), 

The accumulation of substance B in a container gradually changes the milieu of this substance and therefore its potential. For this reason, it is required that amount n and energy are kept small in order to keep the disturbance small. This can be symbolized by An and dlT . itself results as a quotient of both quantities  

It is of course necessary to avoid or subtract all energy contributions due to side effects (e.g., as a result of friction, lifting, entropy transfer, acceleration, production of other substances, solvents, or mixing partners, etc.). If, on the other hand, the process (the transport of substance B) runs spontaneously from left to right, it releases energy. In this case, W n and therefore // are negative but apart from that our considerations remain essentially the same. 

The unit for chemical potential which results from the equation ft = AW JAn is J mol Since we constantly deal with values of the chemical potential, we are justified in giving this unit its own name, Gibbs, abbreviated G, in a manner analogous to Volt for the electric potential difference as we have done in Sect. 4.5  

Naturally, the energy of the portions of the elements taken from the left is to be fotmd in the substance B formed from them. We do not have to worry about these contributions since they drop out when calculating the drive of a transformation of substances. This is so because, as is always the case in chemistry, the elements are conserved (see Sect. 4.4). Only the additional quantity dW which we can identify with fiAn, matters. Together with substance B, it is added to the system on the right and so increases its energy. We could use the increase AW of W to infer the value of AW n = / dn, even if we did not know anything of the existence of the reactor or even if it did not exist at all. 

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