Page 177 - Chemical equilibria Volume 4

Appendix 1

Recap on the Reference

States of Solutions

In this appendix, we recap a few concepts pertaining to solutions, and to
reference states used in the definition of the activities.

A1.1. Concentration and molar fraction

Consider a solution. We label the values relative to the solvent with the
subscript 0, and those relative to the solutes with the subscript s. By
definition of the molar fractions, we can write the ratio:

x s = n s [A1.1]
x 0 n 0

However, the volume of the solution, as a function of the partial molar
volumes of the components, is given by:

0 ∑
V = n V + n V s [A1.2]
s
0
s
Therefore, by using the relation defining the concentration, we find:

n n x
C = s = s = s [A1.3]
0 ∑
0 ∑
s
V nV + n V s x V + x V s
0
s
0
s
s s
Chemical Equilibria, First Edition. Michel Soustelle.
© ISTE Ltd 2015. Published by ISTE Ltd and John Wiley & Sons, Inc.