# Mass Transfer Questions and Answers – Molecular Diffusion in Solids

This set of Mass Transfer Multiple Choice Questions & Answers (MCQs) focuses on “Molecular Diffusion in Solids “.

1. Find the operation where diffusion of solids not occurs
b) Leaching
c) Drying
d) Distillation

Explanation: Distillation is the liquid-liquid operation where no diffusion on solid is possible.

2. Find the diffusivity through slab if N flux of A 4 mol/sq.m sec, concentration difference is 2mol/cu.m and distance is 3 m.
a) 2 sq.m/s
b) 4 sq.m/s
c) 6 sq.m/s
d) 8 sq.m/s

Explanation: N flux of A= D(AB)/z * concentration difference
D(AB) = 6 sq.m/sec.

3. Find the activated diffusivity of carbon if energy of activation is 6 kJ; the value of constant diffusivity is 2.5 sq.m/sec. (Hint: the value of exponential of (-6/RT) is 2.55)
a) 6.375 sq.m/s
b) 1.02 sq.m/s
c) 15.3 sq.m/s
d) 16.25 sq.m/s

Explanation: Activated diffusivity= constant diffusivity * exponential value
= 2.5 * 2.55
= 6.375.

4. The term activated means _____________
a) Pressure dependency
b) Temperature dependency
c) Volume dependency
d) None of the mentioned

Explanation: Activated represents the activation energy which depends on temperature.

5. If the two gases are separated by a polymer membrane, the extent of diffusion depends on _______ law.
a) Hendy
b) Raoult
c) Newton
d) None of the mentioned

Explanation: Concentration is directly proportional to pressure so Hendry law is applicable.

6.For permanent gases diffusivity the order is _________ sq.m/s
a) 10-7
b) 10-8
c) 10-9
d) 10-10

Explanation: The gas can become permeable to certain substance if it is in an order of 10-10.

7. The solute movement of fluid on solids are __________
a) Hygrodynamic
b) Hydrodynamic
c) Fluid dynamic
d) None of the mentioned

Explanation: Solute movement is due to pressure difference which is hydrodynamic.

8. If the pore of the solid is inaccessible to external fluids then it is known as dead end.
a) True
b) False

Explanation: If the pore of the solid is inaccessible to external fluids then it is known as isolate.

9. Macroporic surrounding of microscopic pellets powders of different magnitude in size is _______
a) Disperse
b) Bi-disperse
c) Tri-disperse
d) None of the mentioned

Explanation: The double surrounding of these pellets is known as bi-disperse.

10. Find the permeability if diffusivity is 2 units and solubility coefficient is 5 units assume all are in SI units.
a) 10 units
b) 2.5 units
c) 0.4 units
d) None of the mentioned

Explanation: Permeability = solubility co-efficient * diffusivity
= 2 * 5 =10 units.

Sanfoundry Global Education & Learning Series – Mass Transfer.

To practice all areas of Mass Transfer, here is complete set of 1000+ Multiple Choice Questions and Answers