Quizsummary
0 of 20 questions completed
Questions:
 1
 2
 3
 4
 5
 6
 7
 8
 9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
Information
MASS TRANSFER TEST 1
You have already completed the quiz before. Hence you can not start it again.
Quiz is loading...
You must sign in or sign up to start the quiz.
You have to finish following quiz, to start this quiz:
Results
0 of 20 questions answered correctly
Your time:
Time has elapsed
You have reached 0 of 0 points, (0)
Average score 

Your score 

Categories
 Not categorized 0%
Pos.  Name  Entered on  Points  Result 

Table is loading  
No data available  
 1
 2
 3
 4
 5
 6
 7
 8
 9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 Answered
 Review

Question 1 of 20
1. Question
1 pointsDetermine the mole fraction of the water vapor at the surface of a lake whose temperature is 15°C and compare it to the mole fraction of water in the lake (Fig. ). Take the atmospheric pressure at lake level to be 92 kPa.
Assumptions 1 Both the air and water vapor are ideal gases. 2 The mole fraction of dissolved air in water is negligible
Correct
SOLUTION The mole fraction of the water vapor at the surface of a lake and the mole fraction of water in the lake are to be determined and compared
Analysis The air at the water surface will be saturated. Therefore, the partial pressure of water vapor in the air at the lake surface will simply be the saturation pressure of water at 15°C
Pvapor=Psat @ 15°C=1.705 kPa
Assuming both the air and vapor to be ideal gases, the mole fraction of water vapor in the air at the surface of the lake is determined from
yvapo=Pvapor/P=1.705 kPa/92 kPa=0.0185 (or 1.85 percent)
Water contains some dissolved air, but the amount is negligible. Therefore, we can assume the entire lake to be liquid water. Then its mole fraction becomes
ywater, liquid side≅ 1.0 (or 100 percent)
Incorrect
SOLUTION The mole fraction of the water vapor at the surface of a lake and the mole fraction of water in the lake are to be determined and compared
Analysis The air at the water surface will be saturated. Therefore, the partial pressure of water vapor in the air at the lake surface will simply be the saturation pressure of water at 15°C
Pvapor=Psat @ 15°C=1.705 kPa
Assuming both the air and vapor to be ideal gases, the mole fraction of water vapor in the air at the surface of the lake is determined from
yvapo=Pvapor/P=1.705 kPa/92 kPa=0.0185 (or 1.85 percent)
Water contains some dissolved air, but the amount is negligible. Therefore, we can assume the entire lake to be liquid water. Then its mole fraction becomes
ywater, liquid side≅ 1.0 (or 100 percent)

Question 2 of 20
2. Question
1 pointsConsider a nickel plate that is in contact with hydrogen gas at 358 K and 300 kPa. Determine the molar and mass density of hydrogen in the nickel at the interface (Fig.) (answer upto three decimal)
Assumptions Nickel and hydrogen are in thermodynamic equilibrium at the interface
Correct
SOLUTION A nickel plate is exposed to hydrogen. The molar and mass density of hydrogen in the nickel at the interface is to be determined.
Analysis Noting that 300 kPa 3 bar, the molar density of hydrogen in the nickel at the interface is determined BY
That is, there will be 0.027 kmol (or 0.054 kg) of H2 gas in each m3 volume of nickel adjacent to the interface.
Incorrect
SOLUTION A nickel plate is exposed to hydrogen. The molar and mass density of hydrogen in the nickel at the interface is to be determined.
Analysis Noting that 300 kPa 3 bar, the molar density of hydrogen in the nickel at the interface is determined BY
That is, there will be 0.027 kmol (or 0.054 kg) of H2 gas in each m3 volume of nickel adjacent to the interface.

Question 3 of 20
3. Question
1 pointsPressurized hydrogen gas is stored at 358 K in a 4.8mouterdiameter spherical container made of nickel (Fig. ). The shell of the container is 6 cm thick. The molar concentration of hydrogen in the nickel at the inner surface is determined to be 0.087 kmol/m³. The concentration of hydrogen in the nickel at the outer surface is negligible. Determine the mass flow rate of hydrogen by diffusion through the nickel container.
Assumptions 1 Mass diffusion is steady and onedimensional since the hydrogen concentration in the tank and thus at the inner surface of the container is practically constant, and the hydrogen concentration in the atmosphere and thus at the outer surface is practically zero. Also, there is thermal symmetry about the center. 2 There are no chemical reactions in the nickel shell that result in the generation or depletion of hydrogen.
Properties The binary diffusion coefficient for hydrogen in the nickel at the specified temperature is 1.2 x 10^12 m²/s (Table ).
Correct
SOLUTION Pressurized hydrogen gas is stored in a spherical container. The diffusion rate of hydrogen through the container is to be determined.
Analysis We can consider the total molar concentration to be constant (C= CA + CB ≅CB constant), and the container to be a stationary medium since there is no diffusion of nickel molecules (NB =0) and the concentration of the hydrogen in the container is extremely low (CA « 1).Then the molar flow rate ofhydrogen through this spherical shell by diffusion can readily be determined from
Ndiff=4πr1r2DAB CA1,CA,2/r2r1=4π(2.34 m)(2.40 m)(1.2 x 10^12 m² /s) (0.087 0) kmol/m³/2.40 – 2.34=1.228 x 10^10 kmol/s
The mass flow rate is determined by multiplying the molar flow rate by the molar mass of hydrogen, which is M= 2 kg/kmol,
mdiff=MNdiff= (2 kg/kmol)(1.228 x 10^10 kmol/s)=2.46 x 10^10 kg/s
Incorrect
SOLUTION Pressurized hydrogen gas is stored in a spherical container. The diffusion rate of hydrogen through the container is to be determined.
Analysis We can consider the total molar concentration to be constant (C= CA + CB ≅CB constant), and the container to be a stationary medium since there is no diffusion of nickel molecules (NB =0) and the concentration of the hydrogen in the container is extremely low (CA « 1).Then the molar flow rate ofhydrogen through this spherical shell by diffusion can readily be determined from
Ndiff=4πr1r2DAB CA1,CA,2/r2r1=4π(2.34 m)(2.40 m)(1.2 x 10^12 m² /s) (0.087 0) kmol/m³/2.40 – 2.34=1.228 x 10^10 kmol/s
The mass flow rate is determined by multiplying the molar flow rate by the molar mass of hydrogen, which is M= 2 kg/kmol,
mdiff=MNdiff= (2 kg/kmol)(1.228 x 10^10 kmol/s)=2.46 x 10^10 kg/s

Question 4 of 20
4. Question
1 pointsThe composition of moist air is given on a molar basis to be 78 percent N2 Determine the mass fractions of the constituents of air.(answer upto one decimal)
Correct
76.4 percent N2
Incorrect
76.4 percent N2

Question 5 of 20
5. Question
1 pointsThe composition of moist air is given on a molar basis to be 20 percent O2 Determine the mass fractions of the constituents of air.(answer upto one decimal)
Correct
22.4 percent O2
Incorrect
22.4 percent O2

Question 6 of 20
6. Question
1 pointsThe composition of moist air is given on a molar basis to be 2 percent water vapor. Determine the mass fractions of the constituents of air.(answer upto one decimal)
Correct
1.2 percent H2O
Incorrect
1.2 percent H2O

Question 7 of 20
7. Question
1 pointsThe relative humidity of air at 80°F and 14.7 psia is increased from 30 percent to 90 percent during a humidification process at constant temperature and pressure. Determine the percent error involved in assuming the density of air to have remained constant.(answer upto one decimal)
Correct
2.1 percent
Incorrect
2.1 percent

Question 8 of 20
8. Question
1 pointsDetermine the mole fraction of dry air at the surface of a lake whose temperature is 15°C. Take the atmospheric pressure at lake level to be 100 kPa(answer upto one decimal)
Correct
98.3 percent
Incorrect
98.3 percent

Question 9 of 20
9. Question
1 pointsConsider a rubber plate that is in contact with nitrogen gas at 298 K and 250 kPa. Determine the molar of nitrogen in the rubber at the interface.(answer upto four decimal)
Correct
0.0039 kmol/m³
Incorrect
0.0039 kmol/m³

Question 10 of 20
10. Question
1 pointsConsider a rubber plate that is in contact with nitrogen gas at 298 K and 250 kPa. Determine the mass densities nitrogen in the rubber at the interface.(answer upto four decimal)
Correct
0.1092 kg/m³
Incorrect
0.1092 kg/m³

Question 11 of 20
11. Question
1 pointsConsider a carbonated drink in a bottle at 27°C and 130 kPa. Assuming the gas space above the liquid consists of a saturated mixture of CO2 and water vapor and treating the drink as water, determine the mole fraction of the water vapor in the CO2 gas (answer upto two decimal)
Correct
2.77 percent
Incorrect
2.77 percent

Question 12 of 20
12. Question
1 pointsConsider a carbonated drink in a bottle at 27°C and 130 kPa. Assuming the gas space above the liquid consists of a saturated mixture of CO2 and water vapor and treating the drink as water, determine the mass of dissolved CO2 in a 200ml drink. (answer upto two decimal)
Correct
0.36 g
Incorrect
0.36 g

Question 13 of 20
13. Question
1 pointsHelium gas is stored at 293 K in a 3mouterdiameter spherical container made of 5cmthick Pyrex. The molar concentration of helium in the Pyrex is 0.00073 kmol/m³ at the inner surface and negligible at the outer surface. Determine the mass flow rate of helium by diffusion through the Pyrex container.
Correct
7.2 x 10^15 kg/s
Incorrect
7.2 x 10^15 kg/s

Question 14 of 20
14. Question
1 pointsPure N2 gas at 1 atm and 25°C is flowing through a 10mlong, 3cminner diameter pipe made of 1mmthick rubber. Determine the rate at which N2 leaks out of the pipe if the medium surrounding the pipe is a vacuum
Correct
4.48 x 10^10 kmol/s,
Incorrect
4.48 x 10^10 kmol/s,

Question 15 of 20
15. Question
1 pointsPure N2 gas at 1 atm and 25°C is flowing through a 10mlong, 3cminner diameter pipe made of 1mmthick rubber. Determine the rate at which N2 leaks out of the pipe if the medium surrounding the pipe is tmospheric air at 1 atm and 25°C with 21 percent O2 and 79 percent N2.
Correct
9.4 x 10^11 kmol/s
Incorrect
9.4 x 10^11 kmol/s

Question 16 of 20
16. Question
1 pointsA glass of milk left on top of a counter in the kitchen at 25°C, 88 kPa, and 50 percent relative humidity is tightly sealed by a sheet of 0.009mmthick aluminum foil whose permeance is 2.9 x 10^12 kg/s · m² · Pa. The inner diameter of the glass is 12 cm. Assuming the air in the glass to be saturated at all times, determine how much the level of the milk in the glass will recede in 12 h(answer upto five decimal)
Correct
0.00079 mm
Incorrect
0.00079 mm

Question 17 of 20
17. Question
1 pointsA steel part whose initial carbon content is 0.12 percent by mass is to be casehardened in a furnace at 1150 K by exposing it to a carburizing gas. The diffusion coefficient of carbon in steel is strongly temperature dependent, and at the furnace temperature it is given to be DAB 7.2 x 10^12 m² /s.Also, the mass fraction of carbon at the exposed surface of the steel part is maintained at 0.011 by the carbonrich environment in the furnace. If the hardening process is to continue until the mass fraction of carbon at a depth of 0.7 mm is raised to 0.32 percent, determine how long the part should be held in the furnace
Correct
9 h
Incorrect
9 h

Question 18 of 20
18. Question
1 pointsA long nickel bar with a diameter of 5 cm has been stored in a hydrogenrich environment at 358 K and 300 kPa for a long time, and thus it contains hydrogen gas throughout uniformly. Now the bar is taken into a wellventilated area so that the hydrogen concentration at the outer surface remains at almost zero at all times. Determine how long it will take for the hydrogen concentration at the center of the bar to drop by half. The diffusion coefficient of hydrogen in the nickel bar at the room temperature of 298 K can be taken to be DAB 1.2 x 10^12 m²/s.
Correct
3.3 years
Incorrect
3.3 years

Question 19 of 20
19. Question
1 pointsA tank with a 2cm thick shell contains hydrogen gas at the atmospheric conditions of 25°C and 90 kPa. The charging valve of the tank has an internal diameter of 3 cm and extends 8 cm above the tank. If the lid of the tank is left open so that hydrogen and air can undergo equimolar counterdiffusion through the 10cmlong passageway, determine the mass flow rate of hydrogen lost to the atmosphere through the valve at the initial stages of the process.
Correct
4.20 x 10^8 kg/s
Incorrect
4.20 x 10^8 kg/s

Question 20 of 20
20. Question
1 pointsAn 8cminternaldiameter, 30cmhigh pitcher half filled with water is left in a dry room at 15°C and 87 kPa with its top open. If the water is maintained at 15°C at all times also, determine how long it will take for the water to evaporate completely.
Correct
1125 days
Incorrect
1125 days