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Unformatted text preview: where, initially, the total pressure acting on a liquid
surface is the total pressure. Let us denote this pressu re by Pv. The pressure is
then changed by the addition of an inert gas, keeping the temperature fixed, to get
a final total pressure Pt. We wish to find the new value of the equilibrium vapor
pressure P. For this situation, we may integrate this equation above to get
ln æ P ö = RT (P t − P v ),
where we have assumed that the liquid volume does not change with applied
This is called the Gibbs Equation.
Problems 5.5, 5.17 3 5.4. Ideal Solutions: Raoult’s Law:
Consider a solution formed by two miscible liquids A and B. An ideal solution is
one for which
Vsoln = VA + VB. ∆Hsoln = 0. ∆Sm,soln = –R(xAln xA + xBln xB). Gm,soln = RT(xAln xA + xBln xB). Ideal solutions obey Raoult’s law exactly. To state Raoult’s law, let us denote the
mole fractions in the liquid phase by x and the mole fractions in the vapor phase
by y. Also, we denote the v...
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