# Mass Transfer Questions and Answers – Molecular Diffusion in Gas

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

1. __________ energy helps for molecular diffusion.
a) Thermal
b) Electrical
c) Internal
d) All of the mentioned

Explanation: Thermal energy is heat. Heat can cause diffusion among molecules.

2. For two particles at steady state collision of A and B, J flux of A is 2 mol/sq.m sec find the J flux of B.
a) 1
b) 2
c) 3
d) None of the mentioned

Explanation: At steady state collision, J flux of A = – J flux of B = -2.

3. Estimate the mole fraction if concentration of A is 2 mol/cu.m and the total concentration is 5 mol/cu.m.
a) 0.2
b) 0.25
c) 0.4
d) 1

Explanation: xA = cA/C = 2/5 = 0.4.

4. Find the partial pressure of A if the total pressure is 2 atm; Concentration of A is 2 mol/cu.m and total concentration is 5 mol/cu.m.
a) 0.2 atm
b) 0.4 atm
c) 0.6 atm
d) 0.8 atm

Explanation: yA= 2/5 = 0.4
pA = 0.4 x 2 = 0.8 atm.

5. From the reaction, Methane –> Carbon + 2(Hydrogen molecule) find the ratio of N Flux of A to the Total N flux( A+B); Given N Flux of B =-2 N flux of A.
a) 1
b) -1
c) 2
d) -2

Explanation: N flux of A/ Total flux = N flux of A/ N flux of A – 2 N flux of A = -1.

6. For a Steady state diffusion of A through Non- diffusing B. N flux of B= ______
a) 0
b) 1
c) 2
d) Infinity

Explanation: Non- diffusing B means N flux of B = 0.

7. The value of N flux of A under steady state non-diffusing B with diffusing A is _________
a) 0
b) Constant
c) Infinity
d) None of the mentioned

Explanation: Diffusing A with non diffusing B means Flux of A remains Constant while the Flux of B is 0.

8. If the value of N flux of A to the total N flux is 1 then it is a steady state diffusion of non-diffusing B.
a) True
b) False

Explanation: N Flux of A/ Total N flux
For N flux of B = 0 then N flux of A/N flux of A = 1.

Sanfoundry Global Education & Learning Series – Mass Transfer. 