CHEMICAL ENGINEERING REVIEW 2023
CHEMICAL ENGINEERING THERMODYNAMICS PROBLEM SET 2023
1.
A vessel in San Miguel Corp. having a volume of 0.6 m3 contains 3.0 kg of liquid water and water vapour
mixture in equilibrium at a pressure of 0.5 MPa. Calculate the mass of liquid ;
Data: From steam tables, V_g = 0.375, V_f = 0.00109 in m3/kg
a. 1.404 kg
b. 1.230 kg
c. 1.093 kg
d. 0.9733 kg
2.
Dryness fraction of steam is defined as
a. mass of water vapour in suspension/(mass of water vapour in suspension + mass of dry steam)
b. mass of dry steam/mass of water vapour in suspension
c. mass of dry steam/(mass of dry steam + mass of water vapour in suspension)
d. d. none of these.
3.
A tank of a fermenter radiator having a capacity of 0.05 m3 contains a mixture of saturated water and saturated
steam at a temperature of 245°C. The mass of the liquid present is 10 kg. Find the specific internal energy.
From steam tables, corresponding to 245°C :
psat = 36.5 bar, vf = 0.001239 m3/kg, vg = 0.0546 m3/kg, hf = 1061.4 kJ/kg, hfg = 1740.2 kJ/kg, sf = 2.7474
kJ/kg K, sfg = 3.3585 kJ/kg K.
a.
b.
1329.5 kJ/kg
2182.4 kJ/kg
c. 1023.3 kJ/kg
c. 1155.7 kJ/kg
4.
With increase in pressure
a. enthalpy of dry saturated steam increases
b. enthalpy of dry saturated steam decreases
c. enthalpy of dry saturated steam remains same
d. enthalpy of dry saturated steam first increases and then decreases.
5.
Calcular la cantidad de calor, or heat Q, which should be supplied to 2 kg of water at 25°C to convert it into
steam at 5 bar and 0.9 dry. From Perry’s Handbook, hf = 640.1 kJ/kg ; hfg = 2107.4 kJ/kg:
a. 5389 kJ
b. 4865 kJ
c. 2319 kJ
d. 4384 kJ
6.
Find the heat of 0.10 m3 of wet steam at a pressure of 58.03 psia and dryness fraction 0.8. Also calculate the
heat of 1 m3 of steam. From Perry’s Handbook, vg = 8.316 dm3/kmol, hf = 10.885 kJ/mol , hfg = 38.394
kJ/mol
a. 4687 kJ
b. 6253 kJ
c. 5718 kJ
d, 1897 kJ
7.
The statement, “the internal energy of a perfect gas is a function of the absolute temperature only” is also
referred to as the:
a. Amagat’s Law
c. Kelvin’s Law
b. Joules Law
d. Clausius’ Law
8.
In a 6-cylinder, V-type piston engine the compressed air has an internal energy of 450 kJ/kg at the beginning
of the expansion and an internal energy of 220 kJ/kg after expansion. If the work done by the air during the
expansion is 120 kJ/kg, calculate the heat flow to and from the cylinder in kJ/kg:
a. -210
b. 320
c. – 78
d. 110
9.
A non-flow mass of gas was compressed without friction at constant pressure its initial state of 14.13 ft3 and
15.233 psia was found to change to final state of 7.063 ft3. There was a transfer of 40.29 btu of heat from the
gas during the process. How much did the internal energy of the gas change in btu?
a. 20.38
b. 45.7
c. 13.4
d. 56.7
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10. A spherical balloon of diameter 0.5 m contains a gas at 1 bar and 300 K. The gas is heated and the balloon
is allowed to expand. The pressure inside the balloon is found to vary linearly with the diameter. What would
be the work done by the gas when the pressure inside reaches 5 bar?
a. 3060 J
b. 4320 J
c. 3780 J
d. 4500 J
11. Air enters a compressor at 105 Pa and 25°C having volume of 1.8 m3/kg and is compressed to 5 × 10^5 Pa
isothermally. Determine the heat transferred in kJ/kg.
a. 328.4
b. 289.7
c. 182.3
d. 119.3
12-13:
Helium undergoes a non-flow frictionless process following the pressure-volume relation as P = 5/V
+ 1.5 where P is in bar and V is in m3. During the process the volume changes from 0.15 m3 to 0.05 m3 and
the system rejects 45 kJ of heat.
12. Determine the change in internal energy, kJ;
a. 233
b. 376
c. 519
13. Change in enthalpy:
a. 233
b. 376
c. 519
d. 504
d. 504
14. Iron filings are contained in a cylinder in an atmosphere of oxygen. It combines with oxygen to form ferric
oxide. The pressure inside the cylinder is maintained at 101 kPa. The temperature is kept constant at 298 K
by removing heat. For 2 mol iron reacted, calculate change in internal energy given that 831.08 kJ of heat is
liberated in the process.
a. -560 kJ
b. -764 kJ
c. 828 kJ
d. 932 kJ
15. It is given that 1 kg of gaseous CO_2 contained in a closed system undergoes a reversible process at
constant pressure. During this process 42 kJ of internal energy is decreased. Determine the work (kJ) done
during the process. Take cp = 840 J/kg°C and cv = 600 J/kg°C.
a. -14.5
b. -16.8
c. +23.4
d. +13.4
16-17: A tank contains 0.45 m3 of a hydrogen at 1 × 10^5 N/m2 and 80°C. The gas is compressed to a
volume of 0.13 m3, the final pressure being 5 × 10^5 N/m2. (Take γ = 1.4, R = 294.2 J/kg°C)
Determine :
16. The value of index ‘n’ for compression ;
a. 1.345
b. 1.218
c. 1.296
d. 1.447
17. The increase in internal energy of the gas in kJ;
a. 49.9
b. 35.6
c. 89.3
d. 13.4
18. Air at 102 kPa, 22°C, initially occupying a cylinder volume of 0.015 m3, is compressed reversibly and
adiabatically by a piston to a pressure of 680 kPa. Calculate the work done in kJ.
a. 2.751
b. 3.458
c. 0.578
d. 1.227
19. In a petroleum plant, 1 kg of ethane (perfect) gas is compressed from 110 kPa, 27°C according to a law
pV^1.3 = constant, until the pressure is 6.6 bar. Calculate the heat flow (in kJ/kg) to or from the cylinder
walls. Molecular weight of ethane = 30, cp = 1.75 kJ/kg K.
a. 43.5
b. 22.5
c. 67.8
d. 84.5
20. An ideal gas will undergo a thermodynamic cycle in refrigeration plant , 0.1 m3 of an ideal gas at 300 K and
100 kPa is compressed adiabatically to 800 kPa. It is then cooled at constant volume and further expanded
isothermally so as to reach the condition from where it started. Calculate the total net work done (in kJ) and
heat transferred during the cycle. Assume cp = 14.3 kJ/kg K and cv = 10.2 kJ/kg K:
a. -5.45
b. -8.56
c. -12.3
d. -2.33
21. Supposing that 0.15 m3 of an ideal gas at a pressure of 1.5 MPa and 550 K is expanded isothermally to 4
times the initial volume. It is then cooled to 290 K at constant volume and then compressed back
polytropically to its initial state. Calculate the net heat transferred during the cycle in kJ.
a. 42.5
b. 80.0
c. 68.4
d. 15.6
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22. A rigid tank is divided into two equal parts by a partition. Initially one of the partitions is filled with 10 kg water
at 300.15 K and 101.3 kPa and the other part is evacuated. The partition is then removed and the water is
allowed to fill the entire tank. The water attains the temperature of 300.15 K by exchanging heat with the
surroundings. From steam tables, the specific volume of saturated water and water vapour at 300.15 K are
found to be 1.003 × 10–3 m3/kg and 38.81 m3/kg, respectively and the internal energy values of saturated
liquid and saturated vapour are 113.1 and 2412.6 kJ/kg, respectively. Determine the heat transferred.
a. 200 J
b. 400 J
c. 500 J
d. 800 J
23. Air flows steadily at the rate of 0.5 kg/s through an air compressor. It enters the compressor at 6 m/s with a
pressure of 0.1 MPa and a specific volume of 0.85 m3/kg and leaves at 5 m/s with a pressure of 0.7 MPa and
a specific volume of 0.16 m3/kg. The internal energy of the air leaving is 90 kJ/kg greater than that of the air
entering. Cooling water in a jacket surrounding the cylinder absorbs heat from the air at the rate of 60 kJ/s.
Calculate the power required to drive the compressor:
a. 157.5 kW b. 134.5 kW c. 118.5 kW d. 231.7 kW
24. Superheated steam at a 6.87 bar, 205°C, enters in an insulated nozzle with a velocity of 50 m/s. It leaves at
a pressure of 1.37 bar and a velocity of 500 m/s. From Perry’s Handbook, the corresponding to 6.87 bar, h1
= 51.3 kJ/mol. Determine the exit enthalpy of steam in kJ/mol: a.
58
b. 49
c. 22
d. 41
25. An electric current of 0.5 A from a 12 V supply is passed for 5 minutes through a resistance in thermal contact
with saturated water at 1 atm. As a result, 0.798 g of water is vaporised. Assuming that the water vapour
behaves ideally, calculate the enthalpy change during this process in kJ/mol.
a. 37.9
b. 67.7
c. 41..8
d. 57.8
26. At the entrance to a certain nozzle the enthalpy of fluid passing is 2800 kJ/kg, and the velocity is 50 m/s. At
the discharge end the enthalpy is 2600 kJ/kg. The nozzle is horizontal and there is negligible heat loss from
it. Find the velocity at exit of the nozzle in m/s.
a. 434.5
b. 726.3
c. 219.4
d. 634.4
27. Steam at 18 bar is throttled to 1 bar and the temperature after throttling is found to be 150°C. Calculate the
initial dryness fraction of the steam.
From superheat tables at 1 bar and 150°C, we have h = 2776.4 kJ/kg
At 18 bar : hf = 884.6 kJ/kg, hfg = 1910.3 kJ/kg
a. 0.78
b. 0.99
c. 0.86
d. 0.94
28. Steam initially at a pressure of 1.5 MPa and 0.95 quality expands isentropically to 0.75 Mpa and is then
throttled until it is just dry (saturated vapour). Determine per kg of steam , the change in enthalpy ;
At 1.5 MPa, hf = 844.7 kJ/kg ; Tsat = 198.3°C, sf = 2.3145 kJ/kg K, sg = 6.4406 kJ/kg K, vg = 0.132 m3/kg
At 0.75 bar, hf = 709.3 kJ/kg, Tsat= 167.7°C, hfg = 2055.55 kJ/kg, sf = 2.0195 kJ/kg K, sg = 6.6816 kJ/kg K,
vg = 0.255 m3/kg
a. -231.7
b. -437.9
c. -78.9
d. -133.3
29. A liquid mixture containing 50 mol percent each of benzene and toluene at 313 K is to be continuously flash
vaporised so that 60 mol percent of the feed is vaporised. The residual liquid product contains 35 mol percent
benzene. If the enthalpies per mole of feed, distillate and the residue are respectively 5, 30 and 2 kJ/mol,
calculate the heat added in kJ per mole of vapour product.
a. 46 kJ
b. 20 kJ
c. 23 kJ
d. 34 kJ
30. A vapour at 15 atm and 9°C was allowed to expand adiabatically to a final pressure of 3.00 atm; the
temperature fell by 10 K. Calculate the Joule-Thomson coefficient at 9°C, assuming it remains constant over
this temperature range.
a. 0.33
b. 0.48
c. 0.68
d. 0.83
31. Given that μJT = 1.11 K atm-1 for carbon dioxide (Cp = 0.8436 J/g K), calculate the energy that must be supplied
as heat to maintain constant temperature when 20.0 mol CO flows through a throttle in an isothermal JouleThomson experiment and the pressure drop is 35 atm.
a. 8848.56 J b. 18340.99 J c. 28841.00 J d. 38900.00 J
32. A Carnot heat engine receives heat from a reservoir at 1700°F at a rate of 700 Btu/min and rejects the waste
heat to the ambient air at 80°F. The entire work output of the heat engine is used to drive a refrigerator that
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removes heat from the refrigerated space at 20°F and transfers it to the same ambient air at 80°F. Determine
the total rate of rejection to the ambient air.
a. 4200 Btu/min
c. 4900 Btu/min
b. 5200 Btu/min
d. 5900 Btu/min
33. Water at 368 K is pumped from a storage tank at the rate of 25 m3/h. The motor for the pump supplies work
at the rate of 2 hp. The water passes through a heat exchanger, where it gives up heat at the rate of 42000
kJ/min and is delivered to a second storage tank at an elevation of 20 m above the first tank. What is the
temperature of the water delivered to the second storage tank? Assume that the enthalpy of water is zero at
273 K and the specific heat of water is constant at 4.2 kJ/kg K.
a. 344 K
b. 402 K
c. 301 K
d. 503 K
34. Helium (Cp = 5.1926 kJ/kg K) gas is throttled steadily from 600 kPa and 80°C. Heat is lost from the helium in
the amount of 5.5 kJ/kg to the surroundings at 25°C and 100 kPa. If the entropy of the helium increases by
0.25 kJ/kg K in the valve, determine the exit pressure.
a. 227.89 kPa
c. 356.78 kPa
b. 423.65 kPa
d. 527.97 kPa
35. Calculate the temperature drop of the air expanding through a nozzle adiabatically from a negligible initial
velocity to a final velocity of 325 m/s. Assume that air behaves ideally for which Cp = (7/2)R.
a. -52.45 K
b. -44.45 K
c. -32.45 K
d. -22.45 K
36. Steam at 1800 kPa and 673.15 K steadily enters a nozzle at a rate of 5 kg/s and leaves the nozzle at 1400
kPa with a velocity of 300 m/s. The inlet area of the nozzle is 0.02 m2. Heat losses from the nozzle per unit
mass of the steam are estimated to be 3.3 kJ/kg. Determine the exit temperature of the steam:
a. 702 K
b. 611 K
c. 648 K
d. 543 K
37. Calculate the theoretical flame temperature for CO when burned with 100% excess air when both the
reactants are at 373 K. The heat capacities (J/mol K) may be assumed constant at 29.23 for CO, 34.83 for
O2, 33.03 for N2, and 53.59 for CO2. The standard heat of combustion at 298 K is – 283.178 kJ/mol CO.
a. 1821 K
b. 1450 K
c. 2120 K
d. 2300 K
38. Calculate the entropy change(in kJ/kmol-K) when 1 kmol of an ideal gas at 300 K and 10 bar expands through
a throttle to a pressure of 1 bar, both pressures being maintained constant during the process by suitable
means.
a. 13.5
b. 19.1
c. 21.3
d. 23.6
39. Assuming that air is a mixture of 21% oxygen and 79% nitrogen by volume, calculate entropy(in kJ/kmol) of1
kmol air relative to pure oxygen and nitrogen, all at the same temperature and pressure:
a. 1.02
b. 0.32
c. 0.02
d. 4.27
40. Carbon dioxide at 1 bar and 300 K is to be compressed to a pressure of 10 bar in a single-stage compressor
at a rate of 100 m3/h. Assuming that CO2 behaves as an ideal gas, calculate the temperature of the gas after
compression and the work required. Take Cp/Cv= 1.3.
a. 510 K
b. 670 K
c. 450 K
d. 470 K
41. Consider the compression of air (molecular weight = 29) from 105 Pa at 300 K to 3.6 x 106 Pa in ideal twostage compressor with intercooling. Assume that the temperature of air leaving the intercooler is also 300 K
and that the optimum interstage pressure is used. The compressor is water jacketted and the polytropic
exponent n is 1.30 for both stages. Determine the work of compression per kg of air.
18-20: In a 1-MW steam power plant, superheated steam at 2800 kPa and 598 K enters the turbine and it is
expanded to the condenser pressure of 5 kPa. Assuming an isentropic turbine efficiency of 85% and an
isentropic pump efficiency of 80%, the following data are taken from the steam tables:
Specific volume of saturated liquid at 5 kPa is 1.005 x 10–3 m3/kg.
State of water
Enthalpy
Entropy
(kJ/kg)
(kJ/kg K)
Saturated liquid at 5 kPa
138
0.4764
2562
8.3951
Saturated vapour at 5 kPa
Superheated steam at 2800 kPa
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and 598 K
3063
6.6875
determine the following:
42. The ideal Rankine cycle efficiency for the stated conditions
a. 28%
b. 35%
c. 47%
d. 56%
43. The thermal efficiency of the plant
a. 21.3%
b. 29.7%
c. 32.7%
44. The rate of steam production (kg/h)
a. 2400
b. 3230
c. 4150
For numbers 6 to 9:
d. 36.8%
d. 5690
A steam power plant operates on a Rankine cycle between 7000 kPa and 20 kPa. Steam enters the
turbine and is condensed in the condenser at 20 kPa.
45. If the steam enters the turbine at 7000 kPa and 550°C determine the quality of the steam at the turbineexit.
a. 0.97
b. 0.87
c. 0.77
d. 0.67
46. If the turbine has an efficiency of 75% and the power delivered is 100000 kW, calculate the steam mass flow
rate
a. 250 kg/s
b. 200 kg/s
c. 100 kg/s
d. 50 kg/s
47. Calculate the amount of heat transfer in the boiler. The pump is 75% efficient.
a. 140000 kJ/s
c. 240000 kJ/s
b. 340000 kJ/s
d. 440000 kJ/s
48. Determine the thermal efficiency of the plant.
a. 15%
b. 30%
c. 45%
d. 65%
For numbers 10 to 12:
The compression ratio of an ideal Otto cycle is 8. At the beginning of the compression process, air is
at 100 kPa and 17°C. For air, Cv = 0.7165 kJ/kg K and k =1.40
49. If 800 kJ/kg K and k =1.40.
a. 550 kJ/kg
b. 450 kJ/kg
c. 350 kJ/kg
50. Determine the thermal efficiency of the cycle.
a. 66%
b. 56%
c. 46%
51. Calculate the mean effective pressure for the cycle.
a. 140 kPa
b. 330 kPa
c. 620 kPa
b.
For numbers 13 and 14:
a compression
d. 250 kJ/kg
d. 36%
d. 900 kPa
Air is the working fluid being utilized in an ideal Diesel cycle. The working fluid has a cut off ratio and
ratio of 2 and 18, respectively. For air, Cp=0.240 Btu/lbm R, Cv = 0.171 Btu/lbm R.
52. At the beginning of the compression process, the working fluid is at 14.7 psia, 80°F, and 117 in.3. Calculate
the thermal efficiency of the cycle.
a. 83.2%
b. 73.2%
c. 63.2%
d. 53.2%
53. Determine the mean effective pressure.
a. 58 psia
b. 110 psia
c. 240 psia
d. 320 psia
54. Helium as the working fluid in an ideal Ericson cycle operating between limits of 550 and 3000 R is being
utilized. Calculate the thermal efficiency of this cycle.
a. 92%
b. 82%
c. 72%
d. 62%
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