Page 49 - Chemical equilibria Volume 4

2

Properties of States of

Physico-Chemical Equilibrium

Having set out the conditions of equilibrium of a transformation in
Chapter 1, in this chapter we shall examine certain properties of those states
of equilibrium.

2.1. Laws of displacement of an equilibrium

Consider a system in which a transformation takes place which we
suppose to be at thermodynamic equilibrium at certain variable values. We
propose to examine the state to which the system will evolve if we alter the
values of some of those variables. We shall suppose, for the time being, that
the equilibrium is not broken – i.e. that the new state is also an equilibrium
state. The evolution after equilibrium rupture will be examined later on (see
section 2.6)

2.1.1. General form of the displacement laws

As the system is initially at equilibrium, the affinity of
the transformation is null. As this affinity is a state
function, if we alter one or more of these variables even by an infinitesimal
amount, the affinity varies by dA, and becomes:
=
A 'd A

Chemical Equilibria, First Edition. Michel Soustelle.
© ISTE Ltd 2015. Published by ISTE Ltd and John Wiley & Sons, Inc.