Practice Exams ChE - 27

1. An adiabatic tunnel dryer handles 100 kg of banana chips per batch, reducing the moisture content from 50% to 12% wet basis. Drying takes 10 hours to complete by blowing air at 82ºC and 5% RH. The air leaves the dryer saturated. Assuming that the rate of drying is constant, the volume of air blown is
a. 7840 m^3/hr
b. 222 m^3/hr
c. 250 m^3/hr
d. 7000 m^3/hr

2. A solution containing equimolal O2 and N2 is passed through a membrane to separate O2 from N2. The final product is found to contain 45% O2 and 55%N2. Find the percentage O2 remaining if only 20% of the original solution passed through the membrane.
a. 51%
b. 15%
c. 50%
d. 45%

3. An aqueous solution is absorbing NH3 from an air-NH3 mixture. The air 1 inch above the water surface contains 40% of NH3, while the air at the water surface is 0%. The total pressure of the system is 400 mm Hg and the temperature is 85ºF. The rate of absorption of NH3 across the ½ ft2 of water surface us
a. 0.0155 lbmols/hr
b. 0.0155 lbmols/hr
c. 0.00774 lbmols/hr
d. 0.00774 kg/hr
e. none of these

4. The point at which a distinct break in the curve during the FRP occurs
a. equilibrium moisture content
b. free moisture content
c. critical moisture content
d. second critical moisture content
e. none of these

5. The spectral distribution of a perfect emitter has a maximum and the corresponding wavelength depends on the temperature. The maximum spectral emissive power is displaced to shorter wavelengths with increasing temperature. These statements refer to:
a. Stefan – Boltzmann law
b. Kirchoff’s law
c. Wien’s law
d. Planck’s law
e. none of these

6. The osmotic pressure of a solution containing 0.10 gmol NaCl/1000 g water at 25ºC is
a. 2.44 atm
b. 1.22 atm
c. 4.88 atm
d. none of these

7. The equivalent of 45ºTw in the Baumé scale is
a. 28.32
b. 32.48
c. 26.63
d. 42.56
e. none of these

8. The solubilities of NaNO3 at 40ºC and 10ºC are 51.4% by weight and 44.5% by weight respectively. How many grams of NaNO3 may be crystallized from a 10 kg solution initially saturated at 40ºC, if the temperature of the solution is lowered to 10ºC?
a. 6900
b. 4089
c. 3897
d. 1243
e. none of these

9. A 2nd order reaction involving 2 reactants initially present at 0.10 mol/L is found to be 20% complete in 40 minutes when the reaction temperature is 25ºC and 40% complete in 35 minutes when the reaction temperature is 50ºC. The frequency factor for this reaction is
a. 1.12 x 10^5 L/mol-min
b. 1.12 x 10^5 cal/gmol
c. 1.12 x 10^6 L/mol-min
d. 9 x 10^4 L/mol-min
e. none of these

10. If 20% of pulverized limestone is retained by a 150 mesh screen from an original uniform size of 35 mesh, the energy required in Kw to process 1 ton/hr is
a. 6.25
b. 2.65
c. 8.3
d. 3.8
e. none of these