Page 56 - Chemical equilibria Volume 4

32 Chemical Equilibria
If the component added is a product of the reaction, its stoichiometric
coefficient is positive, and we shall have ℜ> if:
'0
ν i > ∑ ν [2.22]
x i j j
The system will evolve so as to produce the component added.

In the opposite case, the reaction will consume the component added.

Thus, we can definitively see that an equilibrium reacts in a complex way
to the isobaric and isothermic addition of a component and that this behavior
must be studied in each particular case. This study may become tricky in the
case of non-perfect real solutions, for which the expressions of
the derivatives of the chemical potentials in relation to the quantity of the
component in question are complex.

2.1.5. Influence of the addition of an inert component

A component is said to be inert if it plays no part in the writing of the
balance equation for the transformation:

– if that component is pure in its phase, its addition causes no alteration
of the chemical potentials of the other components, which are null in that
phase, and therefore no variation of the affinity. Consequently, that addition
has no influence on the equilibrium, which is not modified;

– if the added component A i belongs to a polycomponent phase with
other active components in the reaction, then relation [2.8] is simplified. If
the stoichiometric coefficient of the component added is null, the condition
of evolution becomes:

− ∑ ν j ∂ μ k ℜ > [2.23]
'0
j n ∂ i

The sum is extended to the lone species intervening in the balance
equation.