The change in the Gibbs energy (dG) is given by.
dG=
Similarly. the change in the Helmholtz energy (dA) is as follows
aA=
where ,G = E,v,u, is the so-called free energy of reaction. And represents the rate of change of G with respect to the advancement of reaction (E), at constant T and p, and also the rate of change of A with respect the advancement of reaction, at
Constant T and V.
The meaning of this equation must be emphasized: ,G is 1 derivative and not an ordinary difference despite the use of ’’ “, as signaled by the subscript r feature.
If there is a proper control of the variables involved, the conditions that the second law establishes for both spontaneous processes and chemical equilibrium (Table 1 ) can be obtained. Furthermore, as
A general equation that embodies the tow conditions for spontaneity outlined in Table I can be obtained:
Similarly, the general equilibrium condition can finally in written as follows