Concise Physical Chemistry

c12 JWBS043-Rogers September 13, 2010 11:27 Printer Name: Yet to Come

12 Solution Chemistry

The concept of the ideal solution is as useful as the concept of the ideal gas, but the

reference states must be very different because a model having no intermolecular

interactions would not be a liquid. The next best thing is to propose a model in which

nochangein molecular forces takes place upon mixing two completely miscible

liquids. In this model, mixing of two ideal liquids would be essentially the same as

mixing of two ideal gases (Section 5.3.1). The enthalpy change would be zero at all

proportions, and the mixing process would be entirely driven by a positive entropy

change.

12.1 THE IDEAL SOLUTION

Theenthalpyof mixing to form an ideal solution

A(pure)+B(pure)→AB(mixed)

is zero because no change takes place in attractive forces upon going from isolated

A and isolated B to AB neighbors in the mixture. On the other hand, the entropy

of a system of two pure isolated liquids A and B, in which an observer knows that

any randomly selected molecule will be either A or B according to which “beaker”

it is drawn from, is replaced by a mixed system of greater disorder where random

Concise Physical Chemistry,by Donald W. Rogers

Copyright©C2011 John Wiley & Sons, Inc.

182