# Chemical Reaction Engineering Questions and Answers – Design of Fluid Fluid Reactors

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This set of Chemical Reaction Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Design of Fluid Fluid Reactors”.

1. State true or false.
In physical absorption of a gas in a liquid, the resistance to transfer of gas to liquid is only in the liquid phase.
a) True
b) False

Explanation: Physical absorption involving the transfer of gas to liquid involves resistances in both gas and liquid phase. Gas film resistance and liquid film resistance are both prominent.

2. Which of the following is not a fluid – fluid reaction?
a) Reaction of chlorine with benzene to produce chlorobenzene
b) Soap formation by action of aqueous alkali on fatty acids
c) Action of ammonia on aqueous nitric acid
d) Combustion of coal

Explanation: None

3. Which of the following is the correct expression of Henry’s law?
a) CA = $$\frac{p_A}{H_A}$$
b) HA = $$\frac{C_A}{p_A}$$
c) pA = $$\frac{C_A}{H_A}$$
d) CA = $$\frac{H_A}{p_A}$$

Explanation: Henry’s law states that at a constant temperature, the gas dissolving in a given volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid. HA is Henry’s law constant.

4. What is the rate expression for physical absorption of a gas A to a liquid based on two film theory? (Where, kAg is the gas film mass transfer coefficient and kAl is the liquid film mass transfer coefficient)
a) -rA = $$\frac{p_A- H_A C_A}{\frac{1}{a} + \frac{1}{k_{Al}a}}$$
b) -rA = $$\frac{p_A- C_A}{\frac{1}{k_{Ag} a} + \frac{1}{k_{Al} a}}$$
c) -rA = $$\frac{p_A- H_A C_A}{\frac{1}{k_{Al}a}+ \frac{1}{k_{Al}a}}$$
d) -rA = $$\frac{H_A C_A}{\frac{1}{k_{Al} a}+ \frac{1}{k_{Al}a}}$$

Explanation: $$\frac{-r_A}{k_{Ag} a}$$ = pA – pAi
$$\frac{-r_A}{k_{Al} a}$$ = CA – CAi. Substituting CA = $$\frac{p_A}{H_A}$$, we obtain -rA = $$\frac{p_A- H_A C_A}{\frac{1}{k_{Al}a}+ \frac{1}{k_{Al}a}}.$$

5. The Enhancement factor in liquid film is the ratio of ____
a) Rate of take up of gas by straight mass transfer to the ate of take up of gas by reaction
b) Rate of take up of gas by reaction to the rate of take up of gas by straight mass transfer
c) Rate of reaction at the interface to the rate of take up of gas by straight mass transfer
d) Rate of take up of gas by straight mass transfer to rate of reaction at the interface

Explanation: Enhancement factor compares the rate of physical absorption to the rate of absorption in the presence of chemical reaction. The value of enhancement factor is greater than or equal to 1.

6. The relationship between enhancement factor and Hatta modulus for pseudo first order reaction is ____
a) E = MH
b) E < 5MH
c) 5E > MH
d) E > 5MH

Explanation: For pseudo first order reaction, enhancement factor is high. The value of enhancement factor is greater than about 5 times the hatta modulus.

7. State true or false.
For instantaneous reaction, E < $$\frac{M_H}{5}.$$
a) True
b) False

Explanation: Instantaneous reaction occurring at the film proceeds by high MH. Enhancement factor is less than Hatta number.

8. For Instantaneous reaction with high concentration of liquid, the correct rate expression is ____
a) kAgpA = -rA
b) kAgpAkAl = -rA
c) $$\frac{k_{Ag} p_A}{k_{Al}}$$ = -rA
d) pAkAl = -rA

Explanation: The concentration of liquid is high. The gas phase resistance controls and hence the overall rate is determined by diffusion of A through gas film.

9. The gas film resistance obtained in percentage if the gas film resistance is 10 hr.m3.Pa/ mol and the total resistance is 20.01 hr.m3.Pa/ mol is ____
a) 49.9%
b) 39.9%
c) 29.9%
d) 19.9%

Explanation: Gas film resistance in percentage = $$\frac{Gas \, film \, resistance}{total \, resistance}$$ × 100 = $$\frac{10}{20.01}$$ × 100 = 49.975%.

10. If E = 104 and MH = 10, the nature of reaction is ____
a) First order
b) Second order
c) Pseudo first order
d) Negative order

Explanation: E > 5MH. The reaction proceeds by pseudo first order mechanism at the interface as 104 > 10.

Sanfoundry Global Education & Learning Series – Chemical Reaction Engineering.

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