Page 38 - Chemical equilibria Volume 4

14 Chemical Equilibria
Thus, the necessary and sufficient condition of thermodynamic
equilibrium is, by definition:
A = 0 [1.51]

and the true meaning of the possibility of occurrence of the transformation is
given by the condition:

A > 0 [1.52]

In light of relations [1.23] and [1.24], these conditions are also written:

For thermodynamic equilibrium:

Δ G = 0 [1.53]
r

or:

N
∑ νμ = 0 [1.54]
k
k
k= 1

For the direction of spontaneous reaction:
Δ G < 0 [1.55]
r

or:

N
∑ νμ < 0 [1.56]
k
k
k= 1

These conditions are independent of the nature of the physico-chemical
transformation and the variables chosen to define the system, provided that
system is home only to a single transformation.

1.5. Heats of transformation

Usually, transformations involve heat exchanges with the outside
environment, which may be due to heat being released (exothermic
transformations) or absorbed (in the case of endothermic transformations).
We shall express those heat exchanges in two important cases.