October 18, 2004
Instructor: Aris Docoslis
Textbook and lecture notes are permitted. No solved problems of any kind are permitted,
including tutorial problems and assigned problems. Red and gold sticker calculators are allowed.
The examination time is limited to 50 minutes.
Please check that your exam contains 2 pages. The exam consists of 3 questions, the value of
which is shown on the examination paper. Attempt all questions.
Please write your student number only on all examination booklets.
Question 1 (40 Marks)
A mixture of 1-chlorobutane(1)/chlorobenzene (2) with total composition of z1=0.6 and z2=0.4 is
allowed to equilibrate inside a drum, where it phase-separates into liquid and vapour. The P-x-y
diagram for this mixture at 90 oC is shown in Figure 1.
(10 Marks) What are the dew and bubble point pressures and compositions for the above mixture
at 90 oC? Please provide graphical estimations only.
(10 Marks) If the drum operates at (T1, P1) = (90 oC, 90 kPa), what are the liquid (xi) and vapour
(yi) phase compositions? A graphical estimation will suffice.
(20 Marks) Looking to further increase the mole fraction of 1-chlorobutane in the vapour, your
assistant suggests a flash drum operation under T2= 100 oC and P2=90 kPa. Perform
the calculations that allow you to examine the validity of her/his claim.
- You can assume that Raoult’s law is valid for this mixture.
- Antoine Equation and Coefficients:
ln P sat / kPa = A - o
A B C
1-chlorobutane 13.9600 2826.26 224.10
chlorobenzene 13.9926 3295.12 217.55
(continued on next page)
Pxy diagram for 1-chlorobutane (1) and chlorobenzene (2) at
T = 90 degC (assuming validity of Raoult's law)
0.00 0.20 0.40 0.60 0.80 1.00
Figure 1: Pxy diagram for 1-chlorobutane(1) and chlorobenzene(2) at T = 90 oC.
Question 2 (40 Marks)
Consider one mole of a pure ideal gas that undergoes a PVT change.
(a) (20 Marks) Show that any differential change in the molar enthalpy of this gas can be described
dH C p dT V T T dP
(b) (20 Marks) Considering that Eqn. (1) is an exact differential expression, show that for this gas:
H V S
Cp T ; T P
P P T
Question 3 (20 Marks)
A binary mixture of components (1) and (2) exists at vapour-liquid equilibrium (VLE). Derive a set
of algebraic equations that allow us to calculate the equilibrium compositions of this mixture in the
liquid (L) and vapour (V) phase (namely, y1, y2, x1, x2), if we know that the chemical potentials (i)
of the components are given by:
Vapour phase Liquid phase
AV RT ln( yi )
AL RT ln( x i )
where A iL (T, P), A iV (T, P) are known quantities.