250+ TOP MCQs on Design of CSTRS in Series and Answers

Chemical Reaction Engineering Multiple Choice Questions & Answers on “Design of CSTRS in Series”.

1. State true or false.
It is preferable to use a number of CSTRs in series to achieve a specific conversion than a single CSTR.
A. True
B. False
View Answer

Answer: A
Explanation: Total volume required to achieve a given conversion is less than the volume of a single CSTR. A number of CSTRs in series approaches Plug Flow behavior.

2. What is the mole balance of a component in a CSTR? (Where F₀ is the molar flowrate of reactant entering and F is the exit molar flowrate)
A. F₀ = FX + F
B. F₀ = FX + F₀
C. F₀ = F₀X + F
D. F₀ = X + F
View Answer

Answer: C
Explanation: The mole balance of a component in a CSTR is given as F₀ = F₀X + F. Molar flowrate of a component A fed to the reactor is the sum of molar flowrate at which A is consumed and molar flowrate at which A leaves the reactor.

3. For ‘i’ CSTRs of variable volume in series, the residence time in the i^th reactor is ____
A. τ_i = (frac{- C_i}{-r_i} )
B. τ_i = (frac{C_{i-1}- C_i}{-r_i} )
C. τ_i = (frac{C_i}{-r_i} )
D. τ_i = (frac{C_{i-1}}{-r_i} )
View Answer

Answer: B
Explanation: For 2^nd reactor in series, the mole balance in 2^nd reactor is vC₁ = vC₂ + (-r₂)V₂.
v is the volumetric flowrate and V₂ is the volume of the 2^nd reactor. Rearranging, (frac{V_2}{v} = frac{C_1- C_2}{-r_2}) , τ2 = (frac{C_1- C_2}{-r_2}.) For i^th reactor in series, τ_i = (frac{C_{i-1}- C_i}{-r_i}. )

4. What is the concentration C₄ at the end of 4^th reactor, for n unequal sized CSTRs in series, where X₄ is the conversion in 4^th reactor?
A. C₄ = (1 – X₄)
B. C₄ = C₀X₄
C. C₀ = C₄ (1 – X₄)
D. C₄ = C₀(1 – X₄)
View Answer

Answer: D
Explanation: Conversion in the 4^th reactor is the ratio of reactant converted in the 4^th reactor to the initial concentration. X₄ = (frac{C_0 – C_4}{C_0}.) Hence, C₄ = C₀(1 – X₄).

6. For equal sized CSTRs in series carrying out 1^st order reactions of constant density, which of the following is true? (k_i is the rate constant in a reactor ‘i’ in series)
A. k₁ ≠ k₂ ≠ … ≠ k_n, τ₁ = τ₂ = … = τ_n
B. k₁ = k₂ = … = k_n, τ₁ = τ₂ = … = τ_n
C. k₁ = k₂ = … = k_n, τ₁ ≠ τ₂ ≠ … ≠ τ_n
D. k₁< k₂< …<k_{n, τ1 = τ2 = … = τn
View Answer</k}

Answer: B
Explanation: All the CSTRs are operated at the same temperature. Hence, k₁ = k₂ = … = k_n. The volume of all the CSTRs is the same, V₁ = V₂ = … = V_n. τ = (frac{V}{v_0},) hence τ₁ = τ₂ = … = τ_n.

7. For very low conversion, the value of Damkohler number is ____
A. ≤0.1
B. >10
C. ≥0.1
D. = 10
View Answer

Answer: A
Explanation: Damkohler number estimates the conversion that can be achieved in a flow reactor. At low conversions nearly 10%, Da≤0.1

8. State true or false.
For different sized CSTRs in series, the best system is the one having a minimum volume for a specific conversion.
A. True
B. False
View Answer

Answer: A
Explanation: The optimum size ratio of CSTRs in series depends on the reaction kinetics. For a first order reaction, equal sized CSTRs are operated. For positive order reactions, smaller CSTR is followed by larger ones.

9. For equal sized CSTRs in series carrying out 1^st order reaction, the concentration at the outlet of n^th reactor is ____
A. C_N = (frac{1}{(1 + τk)^N} )
B. C_N = (frac{C_0}{(1 + τ)^N} )
C. C_N = (frac{C_0}{(1 + k)^N} )
D. C_N = (frac{C_0}{(1 + τk)^N} )
View Answer

Answer: D