NATIONAL UNIVERSITY OF SCIENCE AND TECHNOLOGY
FACULTY OF INDUSTRIAL TECHNOLOGY
DEPARTMENT OF CHEMICAL ENGINEERING
CHEMICAL ENGINEERING THERMODYNAMICS 1B
ECE 2204/TCE 2204
TEST 1
Friday 10 June 2022
ANSWER ALL QUESTIONS
Question 1
a) Define the following terms:
i)
Partial property
[1]
ii)
Chemical potential
[1]
iii)
Excess property
[1]
iv)
Residual property
[1]
b) A stream of nitrogen flowing at a rate of 2 kg/s and a stream of hydrogen flowing
at a rate of 0.5 kg/s mix adiabatically in a steady-flow process. If the gases are
assumed ideal, what is the rate of entropy increase as a result of the process? [5]
Question 2
a) The following reaction reaches equilibrium at 500°C and 2 bar:
4HCl (g) + O2 ( g ) → 2H2O ( g ) + 2Cl2 ( g )
If the system initially contains 5 mol HCl for each mole of oxygen, what is the
composition of the system at equilibrium? Assume ideal gases.
[6]
b) A vessel, divided into two parts by a partition, contains 4 mol of nitrogen gas at
75°C and 30 bar on one side and 2.5 mol of argon gas at 130°C and 20 bar on the
other. If the partition is removed and the gases mix adiabatically and completely,
what is the change in entropy? Assume nitrogen to be an ideal gas with CV =
(5/2)R and argon to be an ideal gas with CV = (3/2)R.
[10]
Question 3
a) A liquid solution of LiCl in water at 25°C contains 1 mol of LiCl and 7 mol of
water. Estimate the heat effect if 1 mol of LiCl⋅3H2O(s) is dissolved isothermally
in a liquid solution of LiCl/water at 25°C containing 1 mol of LiCl and 7 mol of
water.
[10]
b) A binary mixture of benzene (1) and toluene (2) is flashed to 75 kPa and 90°C.
Analysis of the effluent liquid and vapor streams from the separator yields: x1 =
0.1604 and y1 = 0.2919. An operator remarks that the product streams are “offspec,” and you are asked to diagnose the problem.
i)
Verify that the exiting streams are not in binary equilibrium.
[10]
ii)
Verify that an air leak into the separator could be the cause.
[10]
Question 4
a) A single-effect evaporator operating at atmospheric pressure concentrates a 15%
(by weight) LiCl solution to 40%. The feed enters the evaporator at a rate of 2 kg/s
at 25°C. The normal boiling point of a 40% LiCl solution is about 132°C, and its
specific heat is estimated as 2.72 kJ/kg·°C. What is the heat-transfer rate in the
evaporator?
[15]
b) Estimate ϕ1 and ϕ2 by for an equimolar mixture of methyl ethyl ketone(1)/
toluene (2) at 50°C and 25 kPa. Set all kij = 0.
P
P
ln 1 
B11  y 22 12 and ln  2 
B22  y12 12
RT
RT



[10]

Question 5
a) A single-effect evaporator concentrates a 20-wt-% aqueous solution of H2SO4 to
70-wt-%. The feed rate is 15 kg/s, and the feed temperature is 27C. The
evaporator is maintained at an absolute pressure of 10 kPa, at which pressure the
boiling point of 70-wt-% H2SO4 is 102°C. What is the heat-transfer rate in the
evaporator?
[10]
b) An invention provides a process for cracking n-butane over a hexagonal boron
nitride catalyst at 750 K and 1.2 bar to produce olefins. Only two reactions have
favorable equilibrium conversions at these conditions:
C4H10 → C2H4 + C2H6
(I)
C4H10 → C3H6 + CH4
(II)
If these reactions reach equilibrium, what is the product composition?
The equilibrium constants at 750 K are found to be: KI = 3.856 and KII = 268.4
END OF QUESTION PAPER
[10]