10-19-23
ChE 3173 Session 11 – More VLE Problems
1. 8.40 The following plot shows a Pxy phase diagram for a binary mixture of species 1 and 2 at 300
K. Answer the following:
(a) A mixture of 2 mol of species 1 and 1 mol of species 2 exists at 20 kPa. Identify where it is on
the plot in the preceding figure, and label it “A.” What phase or phases are present? What is the
composition of each phase that is present?
(b) You wish to isothermally compress this mixture so that there is 1 total mol of liquid in
equilibrium with 2 mol vapor. What pressure must it be compressed to? Identify where it is on
the plot above and label it “B.” What is the composition of each phase present?
2. 8.33 Consider the system of ethanol (1)–benzene (2) at 25°C. This mixture exhibits an azeotrope
at a mole fraction of x1 = 0.28 and a pressure of 122.3 torr. Determine values for the parameters
in the van Laar equation. Estimate the liquid composition and pressure in equilibrium with a
vapor of y1 = 0.75 at 25°C.
3. 8.17 What is the lowest temperature to which a vapor mixture of 1 mole n-pentane and 2 moles
n-hexane at 1 bar can be brought without forming liquid? Assume the liquid forms an ideal
solution.
4. 8.39 A binary mixture of components a and b contains 1 mol a and 3 mol b in the liquid phase at
25°C and 0.50 bar. The excess Gibbs energy of the liquid mixture can be described by the van
Laar equation with A = 4,010 J/mol and B = 2,501 J/mol. The saturation pressure of a is Psat,a =
575 kPa.
(a) If this mixture is in equilibrium with vapor under these conditions, what is the vapor phase
mole fraction of a?
(b) Determine the saturation pressure of b.