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This set of Separation Processes Multiple Choice Questions & Answers (MCQs) focuses on “Steady-state, Ordinary Molecular Diffusion”.

1. Which of the following is Fourier law of heat conduction?
a) q z = k*dT z/dZ
b) q z = – k*dT z /dZ
c) q z = k*T z /dZ
d) q z = k*dQ z /dZ

Explanation: Fourier’s law of heat conduction states that the heat is directly proportional to change is temperature gradient.

2. Which of the following is correct representation of Fick’s law of diffusion?
a) J z = -D*dc a /dz
b) J z = -D*dT/ds
c) J z = D*dc a /dz
d) J z = -D*c a /dz

Explanation: The molar flux is directly proportional to the concentration gradient.

3. What id D ab called in the Fick’s law?
a) Thermal conductivity
b) Density coefficient
c) Diffusivity
d) Electrical conductivity

Explanation: The constant D ab is called as mutual diffusion coefficient or diffusivity.
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4. Which of the following formulae is right about molar flux?
a) N a = x A N – D ab (dx a /d z )
b) N a = x A N – (dx a /d z )
c) N a = x A N – cD ab
d) N a = x A N – cD ab (dx a /d z )

Explanation: The correct formula for molar flux of a component is N a = x A N – cD ab (dx a /d z ).

5. Which of the following is untrue about equimolar diffusion?
a) N a + N b =0
b) J a = J b
c) N=0
d) N a = -cD BA (dx b /dz)

Explanation: J a = J b durig equimolar diffusion.

6. Which of the following is FALSE about unimolar diffusion?
a) N b = N a
b) N= N a
c) N a = x a N a – cD ab (dx a /dz)
d) X b N a = cD ba (dx b /dz)

Explanation: For unimolar diffusion, N b =0.

7. Why does the diffusion of A with respect to B occur?
d) Due to change in heat

Explanation: Concentration gradient is responsible for diffusion.

8. Which diffusion occurs when turbulent motion is there?
a) Molar diffusion
b) Eddy diffusion
c) Charge diffusion
d) No diffusion

Explanation: Due to turbulence there is a cause of eddy diffusion.

9. When is fick’s law applied?
a) For passive diffusion down the concentration gradient
b) Passive osmosis along concentration gradient
c) Active osmosis along concentration gradient
d) Active and passive movement of molecule along concentration gradient

Explanation: Fick’s law is used when there is passive diffusion down the concentration gradient.

10. Which of the following is TRUE?
a) Mass transfer in ordinary mixture occurs due to temperature gradient
b) Mass transfer is proportional to the area the molecules travel
c) Net transfer stops when concentrations are equal
d) The mass transfer is proportional to the area normal to the direction of mass transfer.

Explanation: The mass transfer is proportional to the area normal to the direction of mass transfer. The areal along the transfer is not considered.

Sanfoundry Global Education & Learning Series – Separation Processes.

To practice all areas of Separation Processes, here is complete set of 1000+ Multiple Choice Questions and Answers.