St. JOSEPH’S COLLEGE OF ENGINEERING
DEPARTMENT OF CHEMICAL ENGINEERING
CH 2351CHEMICAL ENGINEERING THERMODYNAMICS – II
QUESTION BANK 2010 -11
UNIT I PROPERTIES OF SOLUTIONS
PART A
1. What are Partial Molar Properties? Explain with an example.
2. Give the physical meaning of Partial Molar Properties.
3. How do you define the term Chemical Potential?
4. Gibb’s energy function is referred to as generating function. Explain.
5. What is the condition for the Phases to be in equilibrium in a multiple phase system?
6. What are the methods available for determining Partial Molar Properties?
7. Explain the analytical method of determining the Partial Molar Property.
8. Explain the Graphical Method of determining Partial Molar Property.
9. Explain the tangent intercept method used to determine the Partial Molar Property.
10. What are ideal gas mixtures?
11. Clearly distinguish between ideal and non ideal solutions.
12. Define fugacity and fugacity coefficient.
13. What is Lewis Randall Rule?
14. What are excess Properties?
15. Give Gibb’s Duhem’s equation?
16. What is standard State?
17. State Henry’s Law.
18. State Raoult’s Law.
19. Which is the Standard State for gases?
20. Which is the Standard state for liquids and gases?
21. Mention the Characteristics of an ideal solution.
22. What is the phase rule variable for non reacting system? Mention its application.
23. Differentiate between molar volume and partial molar volume,
24. What is the entropy change of Mixing for ideal Solutions?
25. What is the Enthalpy change of Mixing for ideal Solutions?
PART B
1. Derive the Gibbs - Duhem’s equation from the fundamentals of thermodynamics and
Show the various forms also.
2. How are the partial molar volumes of the constituents of a binary mixture related to
their mole fractions of the constituents and the molar volume of the solution? Explain
how these equations are useful for the determination of partial molar volumes by the
tangent intercept method.
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3. (a). Show that the rate of change of chemical potential of a substance with pressure is
equal to its partial molar volume in the solution.
(b). Discuss the Gibbs – Duhem’s equation and its various forms. What are the major
fields of application of the Gibb’s Duhem’s equation?
4. (a). Discuss the methods of determining the partial molar properties.
(b). “Chemical potential as a criterion for phase equilibrium” - Explain.
5. (a). State Henry’s law and show that the Raoult’s law is a special case of the Henry’s
law.
(b). All Property changes of mixing are zero for ideal solutions? Do you agree? Explain.
6. Show that (a). The Partial molar mass of a species in solution is equal to its molar mass.
(b). A partial Specific property of a species in solution is obtained by division of the
partial molar property by the molar mass of the species.
7. (a). Derive the Gibb/Duhem equation relating the molar and partial molar property.
(b). Define Fugacity, fugacity co effieicient and Poynting factor of pure species.
8. A rigid and insulated tank is divided into two compartments. One compartment of
volume 1 m3 contains air (Cp = 29.1 J/mol K; Cv = 20.786 J/mol K ) at 300 K and 1 bar
while the second compartment of volume 2 m3 contains helium (Cp = 20.786 J/mol K, Cv
= 12.4712 J/ mol K ) at 100 K and 5 bar. The gases are allowed to mix by removing the
partition. Determine (a) the molar composition of the mixture (b) the final temperature
and pressure of the mixture (c) the change in entropy of Helium and air and (d) the net
entropy change.
9. A rigid tank of 1 m3 volume contains a mixture of molar composition 30% methane and
45% air at 1 bar and 300 K. It is necessary to change the composition such that the final
mixture contains 60 mole% methane and the tank is always held at 300 K. Determine the
mass of methane to be added into the tank and the final pressure of the gas mixture.
10. A mixture of Methane and Ethane with molar composition of 25% Methane and 75%
Ethane is compressed in a reversible and adiabatic compressor from 1 bar and 300 K to 10
bar. Determine the final temperature of the gas, the change in entropy of the mixture,
change in entropy of methane and the change in entropy of Ethane.
UNIT II PHASE EQUILIBRIA
PART A
1. What do you mean by saying a system is in equilibrium?
2. Define the terms Phase and component.
3. What is the criterion for Phase equilibrium in terms of fugacity and chemical potential?
4. Define Gibb’s Phase rule.
5. Write Clapayron equation and explain the terms involved.
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6. What are assumption with which Clapayron equation yields Clausius – Clapayron
equation?
7. Give Clausius Clapayron equation and explain the terms.
8. State Duhem’s theorem.
9. Give the importance of Vapor liquid equilibrium.
10. Give the fundamental relationship in the study of VLE.
11. What is the criterion applicable for low pressure VLE problems?
12. What is Boiling point diagram?
13. What is Poynting correction?
14. What is equilibrium diagram?
15. Differentiate between minimum boiling and maximum boiling azeotropes?
16. What are azeotropes? Give examples.
17. What is the effect of pressure on azeotropes?
18. Define Bubble point and dew point temperatures.
19. What are partially miscible and immiscible systems? Give an example each.
20. What are the applications of Ternary liquid equilibrium?
21. Draw PTxy diagram for low boiling azeotrope.
22. Write any two activity composition models.
23. Write down the condition of Criteria for liquid/liquid equilibrium.
24. What are partially miscible systems? Give examples.
25. Give the applications of Clausius Clapayron equation
PART B
1. (a). What do you mean by positive and negative deviation from ideality? “ A solution
exhibiting positive deviation from ideality is formed accompanied by an absorption of
heat and a solution exhibiting negative deviation from ideal behavior if formed
accompanied by an evolution of heat”. Explain.
(b). Why does the boiling point diagram at a higher pressure lie above that at a lower
pressure?
2. (a). What do you understand by the number of degrees of freedom? How is it
determined using the phase rule for a non-reacting system?
(b). What are the available degrees of freedom in the following non-reactive equilibrium
systems?
(i). Two miscible liquid phases, each containing the same three liquid phases.
(ii). A vapor phase containing ammonia in air and a liquid phase containing ammonia in
water at a specified temperature.
(iii). A mixture of Benzene and Toluene undergoing a simple distillation operation.
3. (a). The binary system, acetone (1) – acetonitrile (2) confirms closely to Raoult’s law.
Using the vapor pressure data given below plot the following
(a). P – x1 and p – y1 curves at 323 K
(b). T – x1 and T – y1 curves at 53.32 kPa
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------------------------------------------------------------------------------------------------------------T, K 311.45
315
319
323
327
331
335.33
P1S kPa53.32
61.09
70.91
81.97
94.36
108.2
124.95
P1S kPa21.25
24.61
28.90
33.79
39.35
45.62
53.32
------------------------------------------------------------------------------------------------------------(b). Assuming Raoult’s law to be valid for the system Benzene (1) –Ethyl Benzene (2) and
the vapor pressures are given by the Antoine equations.
2788.51
Ln Ps1 = 13.8858 - ----------T – 52.41
3279.47
Ln Ps2 = 14.0045 - ----------T – 60.00
Where P is in kPa and T is in K. Construct the following
(a). The P –x-y diagram at 373 K
(b). The T– x-y diagram at 101.3 kPa
4. (a). What are the critical solution temperature and the three-phase temperature with
reference to partially miscible liquid systems.
(b). How would you estimate the composition of the Vapor phase in equilibrium with two
immiscible liquid phases?
5. The T – x – y data for the system metaxylene (1) – Propionic acid (2) at 101.3 kPa is
given below
------------------------------------------------------------------------------------------------------------T, K 412.6
411.1
408.4
407.1
408.8
411.7
x1
0.035
0.090
0.258
0.652
0.877
0.989
y1
0.064
0.133
0.314
0.621
0.821
0.975
------------------------------------------------------------------------------------------------------------Does the System form an Azeotrope? Give reasons
6.(a). Distinguish between minimum boiling and maximum boiling azeotropes with the
help of phase diagrams.
(b). Prove that multiple phases at the same T and P are in equilibrium when chemical
potential of each species is the same in all phases.
7. An equimolar solution of Benzene and Toluene is totally evaporated at a constant
temperature, the vapor pressure of benzene and toluene are 135.4 and 54 kPa respectively.
What are the pressures at the beginning and the end of the vaporization process.
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8. (a). Discuss in detail the classification of liquid liquid mixtures with examples.
(b). State the procedure of plotting a triangular graph for a ternary system in equilibrium.
9. Prove that if Raolult’s law is valid for one constituent of a binary mixture over the
whole concentration range it must also apply to the other component.
10. (a). Derive Clausius Clapayron equation.
(b). Discuss the effect of pressure and temperature on Azeotropes.
UNIT III CORRELATION AND PREDICTION OF PHASE EQUILIBRIA
PART A
1. How do you mean by Activity? Give the importance of activity.
2. What is the effect of pressure of activity?
3. How do you define the activity of a component in a solution?
4. What do you mean by activity coefficients?
5. What is the effect of pressure on activity coefficients?
6. What is the effect of Temperature on activity coefficients?
7. Give the importance of Gibbs-Duhem’s equation.
8. What are activity coefficient equations? Give an example.
9. Give Margules equation and Van Laar equation.
10. Give Wilson’s equation.
11. What do you mean by Consistency tests?
12. What is co-existence equation?
13. Explain zero area method for testing the consistency of VLE data?
14. Give NRTL equation.
15. What are Uniquac and Unifac method?
16. Name local composition models for activity coefficients.
17. Which is the most reliable method for testing the consistency of experimental VLE
data?
18. How can you test the consistency data using partial pressure data?
19. How can you calculate the activity coefficient using Gibbs-Duhems equation?
20. How would you estimate the composition of the vapor phase in equilibrium with two
Immiscible liquid phases.
21. List out the different tests available for testing the consistency of VLE data.
22. What do you mean by excess property?
23. What is the difference between Activity Composition models and Local composition
models?
24. Write down any two activity composition models.
25. Explain the importance of GE/RT term.
PART B
1. (a).How are the Gibbs-Duhem equations helpful in testing the consistency of the VLE
data?
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(b). What is the zero method for testing the consistency of VLE data?
2. (a) Derive the Coexistence equation
(b) X - Y forms azeotrope at 25oC containing 80% X. Find Van Laar constants. The vapor
pressure of X and Y at 25oC is 700 and 710 mmHg. Total Pressure is 760 mmHg. What is
the composition of a vapor in equilibrium with liquid containing 30% X?
3. (a).
Describe the methods for testing the Thermodynamic Consistency of
experimentally determined VLE data for Binary systems.
(b). Discuss about the Various Activity Coefficient Composition models and their
applications in analyzing the Phase equilibrium for Binary systems under Isothermal and
Isobaric conditions.
4. (a) Explain in detail about ternary LLE.
(b) Calculate the vapor phase composition of Benzene and Toluene mixture in equilibrium
with Liquid mixture at 1atm and 92oC. Pure component vapor pressures of Benzene and
Toluene at 92oC are 1078 and 432 mmHg respectively.
5. Water (1) - Hydrazine (2) system forms an azeotrope containing 58.5mole% hydrazine
at 393K and 101.3KPa. Calculate the equilibrium vapor composition for a solution
containing 20mole% hydrazine. The relative volatility of water with reference to
hydrazine is 1.6 and may be assumed to remain constant in the temperature range
involved. The vapor pressure of hydrazine at 393K is 124.76Kpa.
6. Two components A & B form a maximum boiling azeotrope at 90o C and 100 KPa.
The composition of the azeotrope is 60 mole% A. The vapor pressures of A and B at 90 o
C are 79 KPa and 39.5 KPa respectively. Check whether the activity coefficient of this
solution can be represented by Margules equation.
7. The system acetone (1) & Cyclohexane (2) forms an azeotrope at x1 = 0.7390 at 25o C
and 262 Torr. Estimate by Vanlaar constants for the system and calculate the activity
coefficients at x1= 0.5
8. The VanLaar constants A & B for the system 1-propanol –Chlorobenzene are 1.1239
and 1.2586. Calculate γ1 & γ1., when x1 = 0.2, 0.4, and 0.6.
9. The Vanlaar constant A and B for the system Ethanol – Benzene at 50o C are 1.7910
and 1. 8262 respectively. Estimate the activity coefficients of the components in a
solution containing 60 mole% Ethanol.
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10. From the data check whether the system is consistent or not
X1 = 0
γ1 = 0.576
γ2 = 1.00
0.2
0.655
0.985
0.4
0.748
0.930
0.6
0.856
0.814
UNIT-IV
CHEMICAL REACTION EQUILIBRIA
0.8
0.950
0.626
1.0
1.000
0.379
PART-A
1. Explain the criterion of Chemical reaction equilibrium
2. What are Homogeneous and Heterogeneous reactions?
3. What are Single and Multiple reactions?
4. What is meant by Set of Primary reactions?
5. Explain the activities of reactants and products.
6. Explain the term “Reaction co-ordinate”
7. Write a note on the choice of Standard State in the study of Chemical reactions.
8. Explain Equilibrium constant
9. What are the various methods to compute equilibrium constant?
10. What are the applications of equilibrium constant?
11. What is the effect of temperature on equilibrium constant?
12. In what type of reactions, is the equilibrium constant independent of temperature?
13. What is the effect of Pressure on Reaction Equilibrium constant?
14. What is the relation between Ka, Ky and K?
15. Define Standard Free Energy and how it is related to equilibrium constant?
16. Is the Gibbs free energy change of a chemical reaction related to the work done by
the system? Give an example.
17. Explain the term “ Equilibrium Conversion”
18. What reaction conditions affect the equilibrium conversion in chemical reactions?
19. What is the effect of Pressure on the Degree of conversion at equilibrium, for a gas
phase reaction?
20. What is the effect of Inert on equilibrium conversion?
21. Write the relation between Equilibrium constant and standard free energy change.
22. What do you mean by the term “feasibility of a reaction”
23. How will you estimate the standard heat of reaction at temperature T given the
standard heat of reaction?
24. What is the effect of Pressure on Equilibrium composition?
25. List out the factors affecting Equilibrium Conversion.
PART-B
1. For the reaction SO2 + ½ O2
SO3 in equilibrium at 900K, What pressure is
required for a 90% conversion of SO2, if the initial mixture is equimolar in the
reactants. Take Ka = 1.3 at 900K.
2. (a) Explain the effect of reaction conditions on equilibrium.
(b) Compute the equilibrium constant for the water gas reaction at 540oC
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CO + H2O
CO2 + H2
Data:
Component:
Gf (cal / gmol):
CO
-26420
H2O
-57800
CO2
-94050
H2
0
3. Ethanol can be manufactured by the vapor phase hydration of Ethylene
according to the reaction.
C2H4 (g) + H2O (g)
C2H5OH(g)
The feed to a reactor in which the above reaction takes place in a gas mixture
containing 25 mole% Ethylene and rest of Steam. Estimate the product
composition, if reaction occurs at 125oC and 1atm. The value of Go for the
above reaction at 125oC is 1082calories.
4. (a) Explain Homogeneous and Heterogeneous reactions with suitable examples .
(b) For a reaction, A
2B the equilibrium constant at 500oC is 0.3. The
standard heat of reaction is 500 Kcal/Kgmole. Calculate, making suitable
assumptions, the equilibrium constant at 200oC.
5. (a) Derive the expression relating equilibrium constant and standard free energy
change from the fundamentals of thermodynamics.
(b) Develop the expression giving the reaction equilibrium constant (K) in terms of
the reactants and products in the case of a homogeneous chemical reaction.
6. Calculate the equilibrium percentage conversion of Nitrogen to Ammonia at 700K
and 300atm, if the gas enters the converter with a composition of 75mole% H2 and
rest N2. The reaction is
N2 + 3H2
2NH3
Data: At 700K and 300atm,
The reaction equilibrium constant, K = 0.0091
The correction term for Fugacity coefficients, K = 0.72
7. A gas mixture containing 25% CO, 55% H2 and rest inerts is used for Methanol
synthesis at 300bar and 623K. If the gases coming from the catalyst chamber is in
chemical equilibrium with respect to the reaction
CO + 2H2
CH3OH
What percent of CO would have been converted, if Ka = 1.4 x 10-4.
8. Pure N2O4 at a low temperature is diluted with air heated to 25oC and 1atm.
The mole fraction of N2O4 in the N2O4 - Air mixture before dissociation begins
is 0.20. W hat is the extent of the decomposition and what are the moles fractions of
N2O4 and NO2 present at equilibrium? The reaction equilibrium constant Ka =
0.154
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9. Compute the equilibrium mole fraction of each of the species in the gas phase
reaction
CO2 + H2
CO + H2O at 1000K and at (a) 1atm total
pressure and (b) 500atm total pressure. The reaction equilibrium constant K a =
0.698 at 1000K. Standard state is pure gas at 1000K and 1atm. Initially there are
equal
amounts of CO2 and H2 present. The fugacity coefficients at 500atm for the
species
are; CO2 = 0.99, H2 = 1.15, CO = 1.08 and H2O = 0.86.
10. The dissociation of N2O4 into NO2 is carried out at 25oC and 2atm, according to
reaction N2O4
2 NO2, W hat is the molal ratio of NO2 and N2O4 in the
product on the basis of one mole of N2O4?
Data: At 298K,
Hof for N2O4 = 23.491Kcal / g mol
Hof for NO2 = 12.390 Kcal / g mol
UNIT-V
REFRIGERATION & LIQUEFACTION
PART-A:
1. Explain the principle of Refrigeration
2. Explain one ton of refrigeration
3. What are the requirements for a good refrigerant?
4. Name few refrigerants and their relative advantages.
5. Name different components of an air-refrigeration cycle.
6. Give P-H diagram of a vapor compression cycle.
7. Explain C.O.P. and refrigeration capacity
8. Define compressor efficiency
9. Why is throttling used in practical refrigerators in place of turbine?
10. What is a vapor-compression refrigeration cycle?
11. Give the schematic diagram of an absorption refrigeration unit.
12. What is meant by absorption refrigeration?
13. What is Heat pump?
14. What are the various Liquefaction processes?
15. Name various methods with which liquefaction can be accomplished.
16. Define Joule-Thomson expansion
17. Explain Linde liquefaction process
18. Explain Claude liquefaction process
19. Define Cycle efficiency
20. Define Practical efficiency.
21. What is an Air standard diesel dual cycle?
22. What are Otto and Diesel cycles?
23. What is the advantage of Claude liquefaction process over Linde Liquefaction
process?
24. What are the factors that are to be considered for selecting a refrigerant?
25. What are the methods to accomplish cooling?
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PART-B:
1. (a) Explain with neat sketch of Vapor - Compression refrigeration process.
(b) A Carnot refrigerator is used to maintain a space at 0oC while the outside
temperature is 25oC. Find C.O.P., mass of refrigerant required and power required
if the capacity is one ton.
2. (a) Explain briefly about the Gas refrigeration process.
(b) An air-refrigeration machine rated at 10ton is used to maintain the temperature
of a cold room at 261K, when the cooling water is available at 293K. The machine
operates between pressures of 1.013bar and 4.052bar. Assume a 5-K approach in
the cooler and the refrigerator. If the specific heat of air may be taken as 1.008 KJ
/ Kg K and  = 1.4, calculate the COP and air circulation rate.
3. (a) Explain in detail about the Absorption refrigeration process.
(b) A refrigeration system operates on the reversed Carnot cycle between 30oC
and -10oC. The capacity is 10tons. Find COP, Heat rejects from the system
per hour and power ratings of the compressor motor, if the overall electro
mechanical efficiency is 90%.
4. (a) A refrigeration system requires 1KW of power for a refrigeration rate of
3KJ/sec. Determine the COP, the heat rejected by the system and the lowest
temperature that can maintain if the heat is rejected at 308K.
(b) An ideal vapor-compression unit with Freon-12 refrigerant operates between
an evaporator temperature of 243K and a condenser temperature of 308K. If the
power
input to the compressor is 50KW, what is the refrigeration capacity in tons
of refrigeration? The enthalpy of saturated liquid Freon-12 at 308K is 69.55KJ/Kg.
The enthalpy of super heated vapor leaving the compressor is 200KJ/Kg.
5. (a). Briefly discuss about the following;
(i) Choice of refrigerant
(ii) Application of refrigeration
(b). Linde process is used for air liquefaction. The high-pressure gas leaving the
compressor is at 120bar and is cooled to 306K (516KJ/Kg) before it is sent through the
heat exchanger where it exchanges heat with low-pressure gas leaving the separator at
2bar. A14 K approach is desired at the hot end of the exchanger so that the lowpressure gas leaving the exchanger is at 292K (526KJ/Kg). Enthalpy of saturated
liquid and saturated vapor at 2bar is 121KJ/Kg and 314KJ/Kg respectively. Determine
(a) the fraction of the air liquefied during expansion and (b) temperature of the air on
the high-pressure side of the throttle valve.
6. (i). Derive the equation for coefficient of performance of the carnot refrigerator.
(ii). What are important properties of a refrigerant.
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7. A refrigeration system requires 1 KW of power for a refrigeration rate of 3 KJ/S.
Determine (i).The coefficient of performance.
(ii). The seat rejected by the system.
(iii).The lowest temp. that the system can maintain if the heat is rejected at 308 K
8. (i). What are the properties of refrigerant.
(ii). Write about Carnot cycle with T S diagram.
9. (i). Explain Rankine cycle.
(ii). Write about dual cycle.
10. The work output of an Ideal Carnot engine operating between two thermal
reservoirs are at 1000K and the other at 300K is utilized to drive the compressor of
a vapor compression refrigeration unit working on Freon – 12. The heat rejected
by the engine is 30 KW. The enthalpy of saturated Freon – 12 liquid at 300 K is
61.9 KJ/Kg and the enthalpy of saturated Freon – 12 vapor at 240 K = 172.8
KJ/Kg. Determine the COP, the refrigerator capacity and the circulation rate of
the refrigerant.
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