
Dilute Solutions 181
later it is not straightforward to convert this intuitive feeling into a sound argument,
even at a qualitative level.
FIGURE 9.2 Vapor pressures
To show that the vapor pressure of
solutions has to be less than the vapor
pressure of solvents, consider a setup as
shown in the next figure. The solvent
extending from A to B is separated from
the solution extending from B to C by
a semi-permeable membrane at B. The
fact that the Osmotic Pressure of the so-
lution is higher than the solvent means
the length of the column BC is greater
than the length of the column AB. If we
choose a point D such that the length
of the column BD equals that of ...