UNIVERSITY OF TECHNOLOGY, JAMAICA

COLLEGE/ FACULTY: Engineering and Computing

SCHOOL/ DEPARTMENT: SOE/Chemical Engineering

Final Examination, Semester 1

Module Name: Chemical Engineering Thermodynamics I

Module Code: ChE3003

Date: JANUARY 2010

Theory/ Practical: Theory

Groups: BENG. 3C

Duration: TWO (2) HOURS

Instructions

1. ANSWER ALL QUESTIONS.

2. EACH QUESTION MUST BEGIN ON A NEW PAGE.

3. LEAVE TWO LINES BETWEEN PARTS OF A QUESTION.

4. SHOW CLEARLY ALL EQUATIONS USED FOR CALCULATIONS.

5. ANSWERS MUST BE NUMBERED IDENTICAL TO THE QUESTION BEING

ANSWERED.

6. THE INTENDED MARK IS INDICATED AT END OF THE QUESTION.

7. A FORMULA SHEET AND UNIT CONVERSION IS ATTACHED.

DO NOT TURN THIS PAGE UNTIL YOU ARE TOLD TO DO SO

A (Multiple choice)Circle the letter that identifies the correct response to the following questions (1×10 =10 mark):

QUESTION 1:

Which of the following is Kelvin’s statement of the second law of thermodynamics.

a. The entropy of the universe increases in a spontaneous process.

b. It is impossible to take heat from a hotter reservoir and completely convert it into work by a

cyclic process without transferring a quantity of heat to a cooler reservoir.

c. It is impossible for a cyclic process to transfer heat from a body at lower temperature to one

at a higher temperature without converting some work to heat.

d. All of the above.

QUESTION 2:

The theory that gases having the same reduced temperature and pressure have similar P-V-T

behaviors is called the _________.

a. state postulate

b. ideal gas law

c. principle of corresponding states

d. Le Chatelier’s Principle

QUESTION 3:

Which of the following is a reversible process?

a. freezing of water at -10oC and 1 atm

b. melting of ice at 0oC and 1 atm

c. melting of ice at 25oC and 1 atm

d. evaporation of water at 25oC and 1 atm

QUESTION 4:

Which of the following is the significance of the third law of thermodynamics?

a. The absolute entropy of a substance decreases with increasing temperature.

b. The change in entropy of the universe must be positive for a spontaneous process.

c. The absolute value of entropy can be measured for some very pure substances.

d. The entropy of the universe is constant.

QUESTION 5:

A Carnot heat engine operates between a heat source at 400 oC and a heat sink at 25 oC. If 0.7 kJ of

heat is rejected to the heat sink, how much work is produced by the engine?

a. 0.557 kJ

b. 1.580 kJ

c. 0.880 kJ

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d. 10.50 kJ

QUESTION 6:

The correct statement about isothermal process is

a. dT = 0

b. dU = 0

c. q = -w

d. All of the above.

QUESTION 7:

If in fixing the state of a substance, the temperature and pressure are specified, then the substance

CANNOT be a _________.

a. superheated gas

b. saturated mixture

c. supercritical vapor

d. sub-cooled liquid

QUESTION 8:

Which of the following is true.

a. Entropy is an intensive property but a state function.

b. Entropy is an extensive property and not a state function.

c. Molar entropy is an extensive property but not a state function.

d. Entropy is an extensive property and a state function.

QUESTION 9:

If 25.0 L of an ideal gas is compressed isothermally under constant atmospheric pressure until the

volume becomes 5 L, the change in internal energy is

a. 20.0 J

b. -2026.5 J

c. +2026.0 J

d. 0.0 J

QUESTION 10:

Which of the following is NOT an intensive property?

a. Entropy

b. Density

c. Temperature

d. Pressure

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SECTION BCircle the true statements but explain the false in the answer booklet provided (2×10 =20 marks):

QUESTION 11:

a. The relative error of the ideal gas approximation compared to the true P-V-T character of

gases usually depends only on the reduced temperature and reduced pressure.

b. For a system to be in thermodynamic equilibrium, the temperature and the pressure have to

be the same everywhere.

c. A quasi-equilibrium process is the same as an equilibrium process.

d. The state of the air in an isolated room is completely specified by the temperature and the

pressure.

e. For a cycle, the net work is always zero.

f. The boundary work associated with constant-volume systems is always zero.

g. Is it impossible to compress an ideal gas isothermally in an adiabatic piston–cylinder device.

h. A thermal-energy reservoir is a body that can supply or absorb unlimited quantities of heat

isothermally.

i. Even in the absence of friction and other irreversibilities, a heat engine cannot have an

efficiency of 100 percent.

j. The ideal-gas assumption is suitable for real gases when it is at a low temperature or low

pressure relative to its critical temperature and pressure.

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SECTION CProvide detailed calculations and diagrams in answering the following questions:

QUESTION 12 (30 Marks)

A closed cylinder of volume 0.1 m3 initially contains 200 grams of H2O at 1bar. To double its pressure, heat is added isochorically as shown on the graph as process 1 2. The system undergoes a final process (the straight horizontal line 2 3) to bring the gas to state 3.

(a.) Determine the quality of the mixture at states 1 and 2. [6]

(b.) Determine the change in the total internal energy ΔU for process 1 2.

[6](c.) Determine the frictionless work done and the heat added for process 1 2.

[6](d.) Determine the frictionless work done during process 2 3.

[3](e.) Determine the temperature at state 3.

[3](f.) Determine the heat added/removed during process 2 3.

[6]

QUESTION 13 (20 marks)

A vessel of volume 2.0 m3 contains 100 kilograms of superheated steam at 400oC.

(a.) Using the steam tables, determine the pressure of the gas. (Instead of interpolating, use the closest value tabulated)

[4](b.) Estimate the pressure of the gas based on the ideal gas assumption and calculate the error of

the assumption. [6]

(c.) Estimate the pressure of the gas based on the Redlich-Kwong equation of state and calculate the error of the approximation.

[10]

QUESTION 14(20 marks)

A 50 kg iron block (cp = 0.45 kJ/kg.°C) and a 20 kg copper block (cp = 0.386 kJ/kg.°C), both

initially at 80°C, are dropped into a large lake at 15°C. Thermal equilibrium is established after a while as a result of heat transfer between the blocks and the lake water. Determine the total entropy change for this process.

[20]

TOTAL MARKS =100

END OF PAPER

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Formula Sheet

W b=−∫1

2

PdV

W b=−P(V 2−V 1)

W b=−P1V 1lnV 2

V 1

=−mRT lnV 2

V 1

y= y f +x ( y g− y f )

Q+W =∆ U +∆ Ek+∆ E p

η= WQH

=QH−QC

QH

=1−QC

QH

η=T H−TC

T H

=1−T C

T H

PV=nRT

Q=mC p ∆ T

∆ S=∫ d Qrev

T

∆ S=m [Cp lnT2

T1

−R lnP2

P1]

Redlich–Kwong equation of state

P= RTv̂−b

− a

√T [ v̂ ( v̂+b)]

a=0.42748 R2T c

2.5

Pc

b=0.08662 R T c

Pc

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