Page 106 - Instant notes

D1
NON-ELECTROLYTE SOLUTIONS

Key Notes
A solution is a mixture of one or more solute(s) (the minority
species) dispersed in a solvent (the majority species). Usually, the
solvent, and hence the solution, is a liquid. In non-electrolyte
solutions, the species are not charged and cannot interact
electrostatically. The composition, which is the relative amount
of solute(s) and solvent in the system, can be defined by the
concentration, c i , of each species, i. Alternative but related
measures of composition are the mole fraction, x i , and the
molality, m i , of a species. Mole fraction is used more generally
for all mixtures, even those where a solution is not formed.
Molality is only rarely used.
The chemical potential, µ i , is the partial molar Gibbs free energy
of a species, i. The total Gibbs free energy of any mixture is
obtained by combining the chemical potentials of all the
constituent species. As with other partial molar properties, the
chemical potential of pure i is usually not equal to the chemical
potential of i in a mixture, due to differences in the molecular
environment. These differences in chemical potential are given
by the variation in the activity of i, a i , which is related to the
chemical potential by the equation ,
where , is the standard chemical potential at an activity of
unity.
Related topics Perfect gases (A1) Phase equilibria (D4)
Free energy (B6) Phase diagrams of mixtures (D5)
Solutions (D2)

Composition

A solution is a mixture of two or more species; this consists of one or more minority
substances, the solute(s), dispersed in a majority substance, present in greater amounts,
the solvent. In the vast majority of solutions, the solvent, and hence the solution, is a
liquid (although solid solutions are possible). The term mixture can also be used more
generally to describe a system with more than one substance, often under conditions that
include approximately equal amounts, where no one substance can be considered the
solvent (see Topics D4 and D5). It is easiest to consider chemical species that have no