Page 28 - Chemical equilibria Volume 4

4 Chemical Equilibria
and:
dn k = ∑ ν ℜ [1.4b]
dt ρ k ρ ρ
In these expressions, dn , ℜ and ν respectively denote the variation
k ρ ρ k ρ
of the quantity of the component A k due to the transformation ρ, the rate of
the transformation ρ and the stoichiometric number relative to component
A k in the transformation ρ. The sum of relation [1.4b] is found for all of the
transformations taking place in the system under study.

1.2. Entropy production during the course of a transformation in
a closed system

Consider the transformation [1R.1]. We respectively denote by d S and
i
d S the contributions to the entropy variation made by the entropy
e
production within the system and the exchanges with the external medium.
The entropy balance at each moment can be written as:

dS = d S + d S [1.5]
e
i
dt dt dt
For our study, we choose as variables the p pertinent intensive variables
Y and the quantities of material whose fluxes are reduced, in a closed
k
system, according to relation [1.3], to the derivative of the extent of the
reaction. We can therefore express the entropy flux on the basis of those
variables, so:

p
d S = ∑ S ∂ dY k + S ∂ dξ [1.6]
1 Y
dt k= ∂ k dt ξ ∂ dt
In addition, the entropy contribution due to the exchanges with the
external environment is linked to the exchanged heat, by:

d S 1dQ
e = [1.7]
dt T dt