# Chemical Reaction Engineering Questions and Answers – Kinetics of Homogeneous Reactions – Ideal Reactor Types

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This set of Chemical Reaction Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Kinetics of Homogeneous Reactions – Ideal Reactor Types”.

1. The combination of ideal reactors among the following is ____
a) Plug flow reactor and batch reactor
b) Batch reactor and mixed flow reactor
c) Plug flow reactor and mixed flow reactor
d) Batch reactor only

Explanation: Batch reactor is an unsteady state reactor. Plug flow reactor and mixed flow reactors operate under steady state conditions.

2. State true or false.
There is no axial mixing in a plug flow reactor.
a) True
b) False

Explanation: There is no mixing of early and later entering fluid in a plug flow reactor. There is no overtaking between the fluid molecules.

3. State true or false.
The average concentration of product is low inside a CSTR.
a) True
b) False

Explanation: There is continuous mixing of all fluid molecules inside a CSTR. As there is continuous recycle, the average concentration is low in the reactor.

4. Which of the following is true for a reaction occurring in a batch reactor?
a) The accumulation term is zero
b) Only the component input term is zero
c) Only the component output term is zero
d) Both the component input and output terms are zero

Explanation: Reaction is carried out in batches. As and when a new batch of reactant is fed to the reactor, the preceding batch product is withdrawn.

5. Which one of the following combinations gives the highest conversion for second order reaction?
a) PFR followed by smaller CSTR followed by a bigger CSTR
b) PFR followed by bigger CSTR followed by a bigger CSTR
c) Smaller CSTR followed by PFR followed by a bigger CSTR
d) Bigger CSTR followed by a PFR followed by smaller CSTR

Explanation: For reactions of order greater than one, higher conversion is achieved in a PFR. Smaller the volume of a CSTR, it tends to behave as a PFR. Hence, for higher conversions, the reactors are arranged in the order PFR followed by smaller CSTR followed by a bigger CSTR.

6. For a PFR, the area under the curve $$\frac{1}{-r_A}$$ vs XA gives ____
a) $$\frac{F_{A_0}}{dV}$$
b) $$\frac{dV}{F_{A_0}}$$
c) dVCA0
d) dVFA0

Explanation: For a PFR, FA0dXA = (-rA)dV. $$\frac{dXA}{(-rA)}$$ gives . Area under the curve gives $$\frac{dV}{FA0}.$$

7. The performance equation of a CSTR is ____
a) $$\frac{F_{A_0}}{V} = \frac{(-r_A)}{X_A}$$
b) $$\frac{F_{A_0}}{V} = \frac{X_A}{(r_A)}$$
c) $$\frac{V}{X_A} = \frac{(-r_A)}{F_{A_0}}$$
d) $$\frac{F_{A_0}}{V} = \frac{X_A}{-r_A}$$

Explanation: For a CSTR, Molar flow rate in = Molar flow rate out + accumulation
FA0 = FA + (-rA)V
FA0 = FA0(1- XA) + (-rA)V
Hence, FA0XA = (-rA)V.

8. The performance equation of a PFR is ____
a) $$\frac{F_{A_0}}{dV} = \frac{dX_A}{(-r_A)}$$
b) $$\frac{dV}{F_{A_0}} = \frac{(-r_A)}{dX_A}$$
c) $$\frac{F_{A_0}}{dV} = \frac{(-r_A)}{dX_A}$$
d) $$\frac{F_{A_0}}{dX_A} = \frac{(-r_A)}{dV}$$

Explanation: FA0dXA = (-rA)dV
The reaction is integrated in the entire volume of reactor. The material balance is carried out in a small differential volume dV.

9. If the conversion of a first order liquid phase reaction occurring in a CSTR is 75%, molar feed rate is 5 mol/min, the rate of the reaction is 5 $$\frac{mol}{litre.min}$$ then the volume of the reactor (in litre) is ____
a) 0.5
b) 0.75
c) 0.33
d) 0.4

Explanation: For a CSTR, the performance equation is FA0XA = (-rA)V
FA0 is molar feed rate and XA is the fractional conversion
5 × 0.75 = 5 × V
V = 0.75 L

10. If CA is the final concentration and CA0 is the initial concentration, the conversion of a reaction is expressed as ____
a) $$\frac{C_{A0}-C_A}{(C_{A0})}$$
b) $$\frac{C_{A0}-C_A}{(-r_A)}$$V
c) $$\frac{C_{A0}-C_A}{(-r_A)V}$$
d) $$\frac{C_A}{(C_{A0})}$$