UNIVERSITY OF TECHNOLOGY, JAMAICA
TUTORIAL
COURSE:
CHE3003 – Chemical Engineering Thermodynamics I
TUTORIAL: Unit 1: Fundamental Concepts & First Law of Thermodynamics
DATE:
August 28, 2023
Thermodynamic Systems
1. Define the following systems as either open, closed, or isolated.
a. A pot with boiling water on a stove
b. A travel mug with a lid
c. A piston
d. A water bottle
e. A chemical reaction observed in a beaker on a lab bench
f. The human body
g. An ice pack used for injuries
h. A closed thermos bottle/vacuum flask
2. How can the open systems of Question 1 be modified to create closed systems?
3. For each of the systems in Question 1, define the system, the surroundings, and the boundary.
4. A can of soda at room temperature is put into the refrigerator so that it will cool. Would you
model the can of soda as a closed system or as an open system? Explain.
5. What is the difference between macroscopic and microscopic forms of energy?
6. Why don’t isolated systems exist in reality?
Properties of Thermodynamic Systems
7. What is the difference between an extensive property and an intensive property?
8. What are the SI units of the following properties?
a.
b.
c.
d.
9. What thermodynamic properties are constant or equal in the following forms of equilibrium?
a. Mechanical
b. Thermal
c. Phase
10. Distinguish between a system that is in thermodynamic equilibrium and one that is in steady state.
11. Consider two systems of ideal gases. System I consists of pure gas A at a given pressure and
temperature. System II contains a mixture of gases A and B at the same temperature and pressure.
If the molecular weight of gas B is larger than gas A, how does the molar density (mol/cm3) of
system I compare to system II? How does the mass density of system I compare to system II?
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12. During a heating process, the temperature of a system rises by 10°C. Express this rise in
temperature in K, °F, and °R.
Ans: ΔT = 10 K = 18°R = 18°F
13. Convert the following temperature readings to Kelvin.
a.
25°C
b.
32°F
c.
90°R
Ans: 298.15 K
Ans: 273.15 K
Ans: 50 K
14. Use linear interpolation to estimate the specific volume of steam at
with data from the steam tables.
P = 1 MPa
P = 1.5 MPa
T = 320°C
0.2678
0.1765
T = 360°C
0.2873
0.1899
[m³/kg]
and
Ans: = 0.19951 m³/kg
15. A gas is contained in a vertical, frictionless piston-cylinder device. The piston has a mass of 4 kg
and a cross-sectional area of 35 cm2. A compressed spring above the piston exerts a force of 60 N
on the piston. If the atmospheric pressure is 95 kPa, determine the pressure inside the cylinder.
Ans: 123.4 kPa
Processes, Paths & Cycles
16. Sketch P-v property diagrams to represent:
a. An isobaric system
b. An isochoric system
17. Sketch a T-v property diagram to represent an isothermal system.
Understanding Energy
18. Calculate the specific kinetic energy of a ball with mass 10 kg and with a velocity of 2 m/s.
Ans: = 4 J/kg
19. If a large stone is dropped from a cliff 10 m high, how fast will it be going when it hits the
ground?
Ans: = 14 m/s
20. Consider a mass of water equivalent to the mass of the stone in Question 19. If the water is
initially at 25°C, how hot does the water become if its internal energy increases by the same
amount?
Ans: T = 25.02°C
21. A site evaluated for a wind farm is observed to have steady winds at a speed of 8.5 m/s.
Determine the wind energy:
a. Per unit mass
Ans: = 36.1 J/kg
b. For a mass of 10 kg
Ans: E = 361 J
c. For a flow rate of 1154 kg/s of air
Ans: = 41.7 kW
22. Portable air conditioning units are commonly used to cool small rooms. Explain the energy
transformation involved during this cooling process.
Heat, Work & Mass Flow
23. Consider an isobaric expansion of a piston-cylinder assembly. Initially, the system contains 1
mole of a gas at 2 bar within a volume of 10 L. The expansion process is initiated by releasing the
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latch. The gas in the cylinder expands until the pressure of the gas matches the pressure of the
surroundings. The final volume is 15.2 L. Calculate the work done by the system during this
process.
Ans: W = –520 J
24. Consider two closed systems A and B. System A contains 3000 kJ of thermal energy at 20°C,
while system B contains 200 kJ of thermal energy at 50°C. Now the systems are brought into
contact with each other. Determine the direction of any heat transfer between the two systems.
Applying the First Law of Thermodynamics
25. A rigid tank contains a hot fluid that is cooled while being stirred by a paddle wheel. Initially, the
internal energy of the fluid is 800 kJ. During the cooling process, the fluid loses 500 kJ of heat,
and the paddle wheel does 100 kJ of work on the fluid. Determine the final internal energy of the
fluid. Neglect the energy stored in the paddle wheel.
Ans: U = 400 kJ
26. Water is being heated in a closed pan on top of a range while being stirred by a paddle wheel.
During the process, 30 kJ of heat is transferred to the water, and 5 kJ of heat is lost to the
surrounding air. The paddle wheel work amounts to 500 Nm. Determine the final energy of the
system if its initial energy is 10 kJ.
Ans: U = 35.5 kJ
27. Air at 1 bar and 25°C enters a compressor at low velocity, discharges at 3 bar, and enters a nozzle
in which it expands to a final velocity of 600 m/s at the initial conditions of pressure and
temperature. If the work of compression is 240 kJ per kilogram of air, how much heat must be
removed during compression?
Ans: Q = –60 kJ/kg
28. Calculate the internal energy and enthalpy changes resulting if air changes from an initial state of
5°C and 10 bar, where its molar volume is 2.312 × 10–3 m³/mol, to a final state of 60°C and 1 bar.
Assume also that air remains a gas for which PV/T is constant and that = 20.785 and =
29.100 J/mol ⋅ K.
Ans: ΔU = 1144.0 J, ΔH = 1601.2 J
29. Air at 10°C and 80 kPa enters the diffuser of a jet engine steadily with a velocity of 200 m/s. The
inlet area of the diffuser is 0.4 m2. The air leaves the diffuser with a velocity that is very small
compared with the inlet velocity. Determine:
a. The mass flow rate of the air (R = 0.287 kPa ⋅ m³/kg. ⋅ K).
Ans: = 78.8 kg/s
b. The temperature of the air leaving the diffuser.
Ans: T = 361 J
30. Air at 100 kPa and 280 K is compressed steadily to 600 kPa and 400 K. The mass flow rate of the
air is 0.02 kg/s, and a heat loss of 16 kJ/kg occurs during the process. Assuming the changes in
kinetic and potential energies are negligible, determine the necessary power input to the
compressor.
Ans: W = 2.74 kW
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