A CSTR operating at steady state processes an exothermic reaction. If the inlet temperature increases by 10°C while maintaining constant coolant flow rate, which parameter is most likely to increase?

The correct answer is B: Conversion. Higher inlet temperature increases reaction rate (via Arrhenius equation) in an exothermic reaction, leading to higher conversion. Heat removal capacity depends on coolant flow and ΔT.

For an isothermal reversible expansion of 2 moles of ideal gas from 10 L to 50 L at 300 K:

The correct answer is C: W = -nRT ln(V_f/V_i) ≈ -12.88 kJ. W = -∫PdV = -nRT ln(V_f/V_i) = -2×8.314×300×ln(5) ≈ -12.88 kJ. Work done by system is negative (work done on surroundings).

The Colburn analogy relates dimensionless groups for mass, heat, and momentum transfer as:

The correct answer is A: j_D = j_H = f/2, where j represents the Colburn factor. Colburn analogy: j_D = (Sh)/(Re·Sc^(1/3)) ≈ j_H ≈ f/2 for smooth surfaces. Useful for correlating data when only one phenomenon is studied.

A series of 3 identical CSTRs in cascade is used to process a first-order reaction with overall conversion X = 90%. Which statement is true?

The correct answer is C: The concentration decreases exponentially along the cascade. For equal volume CSTRs in series processing first-order reaction: C = C₀/(1+kτ)ⁿ, showing exponential decrease in concentration.

Which of the following best describes the Schmidt number (Sc) in mass transfer?

The correct answer is B: Ratio of kinematic viscosity to mass diffusivity. Schmidt number Sc = ν/D_AB where ν is kinematic viscosity and D_AB is mass diffusivity. It represents the relative importance of momentum and mass transport.

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Chemical Engineering
Chemical Reaction Engineering

Process design, thermodynamics, reactions

51 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 21–30 of 51

Topics in Chemical Engineering

All Mass Transfer 100 Heat Transfer 100 Fluid Mechanics 100 Chemical Reaction Engineering 100 Thermodynamics 97

Q.21 Medium Chemical Reaction Engineering

In a plug flow reactor (PFR) processing a first-order irreversible reaction with rate constant k = 0.5 min⁻¹, what is the space-time (τ) required to achieve 80% conversion?

A 3.22 minutes

B 2.89 minutes

C 4.15 minutes

D 1.61 minutes

Correct Answer: A. 3.22 minutes

EXPLANATION

For first-order reaction in PFR: τ = (1/k)ln(1/(1-X)) = (1/0.5)ln(1/0.2) = 2 × ln(5) = 2 × 1.609 = 3.22 minutes

Test

Q.22 Medium Chemical Reaction Engineering

In fermentation processes, the Monod equation describes microbial growth rate kinetics. Which substrate concentration results in 90% of maximum growth rate?

A 9 times K_s

B 5 times K_s

C 3 times K_s

D 1 time K_s

Correct Answer: A. 9 times K_s

EXPLANATION

From Monod equation: μ = (μ_max × [S])/(K_s + [S]). For μ = 0.9μ_max: [S] ≈ 9K_s

Test

Q.23 Medium Chemical Reaction Engineering

For an isothermal CSTR processing a second-order reaction with inlet concentration C_A0 = 1 M and space time τ = 10 seconds, if k = 0.1 L/(mol·s), the outlet concentration is approximately:

A 0.25 M

B 0.33 M

C 0.50 M

D 0.67 M

Correct Answer: B. 0.33 M

EXPLANATION

For CSTR with second-order kinetics: C_A = [-1 + √(1 + 4kτC_A0)]/(2kτ) = [-1 + √(1 + 4)] / 2 ≈ 0.33 M

Test

Q.24 Medium Chemical Reaction Engineering

Which of the following best describes the role of the Damköhler number (Da) in reactor design?

A Compares diffusion time to reaction time scales

B Compares reaction time to residence time scales

C Measures reactor thermal stability

D Determines optimal catalyst loading

Correct Answer: B. Compares reaction time to residence time scales

EXPLANATION

The Damköhler number Da = k·τ (reaction rate constant × residence time) compares reaction kinetics to flow residence time, determining conversion levels in reactors.

Test

Q.25 Medium Chemical Reaction Engineering

In a jacketed CSTR for an endothermic reaction, increasing the heat transfer area per unit volume of reactor primarily affects which parameter?

A Overall reaction order

B Residence time distribution

C Reaction rate and operating temperature stability

D Product selectivity in parallel reactions

Correct Answer: C. Reaction rate and operating temperature stability

EXPLANATION

Increased heat transfer area improves heat supply rate for endothermic reactions, allowing higher operating temperatures with better temperature control and stability.

Test

Q.26 Medium Chemical Reaction Engineering

In the design of a photocatalytic reactor for degradation of pollutants, which parameter has the most significant effect on reaction rate?

A Reactor diameter and length ratio

B Light intensity and wavelength matching photocatalyst absorption

C Reactor material of construction

D Mixing intensity

Correct Answer: B. Light intensity and wavelength matching photocatalyst absorption

EXPLANATION

Photocatalytic reactions fundamentally depend on photon absorption by the catalyst. Light intensity and wavelength matching the bandgap energy are critical for generating electron-hole pairs.

Test

Q.27 Medium Chemical Reaction Engineering

In a fed-batch reactor for ester synthesis, maintaining the molar ratio of reactants at a specific value improves conversion. This strategy is known as:

A Stoichiometric excess feeding

B Semi-batch operation with controlled feeding

C Equimolar co-feeding

D Gradient feeding strategy

Correct Answer: B. Semi-batch operation with controlled feeding

EXPLANATION

Semi-batch reactors where one reactant is added gradually while maintaining optimal molar ratio with other reactants improve selectivity and conversion, especially for reversible reactions.

Test

Q.28 Medium Chemical Reaction Engineering

The autocatalytic reaction A + B → 2B (where B is catalyst) exhibits which characteristic behavior?

A Linear increase in reaction rate with time

B Initial slow rate with subsequent acceleration, then deceleration

C Constant reaction rate throughout

D Exponential decrease in reaction rate

Correct Answer: B. Initial slow rate with subsequent acceleration, then deceleration

EXPLANATION

Autocatalytic reactions show sigmoidal concentration-time curves due to product-catalyzed acceleration followed by deceleration as reactant concentration decreases.

Test

Q.29 Medium Chemical Reaction Engineering

In industrial practice, which method is most effective for controlling selectivity toward desired product in competitive parallel reactions?

A Increasing reactor residence time uniformly

B Using high concentrations of all reactants simultaneously

C Maintaining low concentrations of undesired reactant through controlled feeding

D Operating at maximum possible temperature

Correct Answer: C. Maintaining low concentrations of undesired reactant through controlled feeding

EXPLANATION

For parallel reactions with different orders, maintaining low concentrations of reactants involved in undesired paths (particularly for higher-order undesired reactions) improves selectivity toward desired product.

Test

Q.30 Medium Chemical Reaction Engineering

In the Langmuir-Hinshelwood mechanism for catalytic reactions, what does the parameter K represent in the rate equation r = kK[A]/[1 + K[A]]?

A Equilibrium constant for adsorption

B Rate constant for surface reaction

C Overall reaction rate constant

D Catalyst deactivation constant

Correct Answer: A. Equilibrium constant for adsorption

EXPLANATION

In Langmuir-Hinshelwood kinetics, K is the equilibrium adsorption constant (K_ads) representing the balance between adsorption and desorption on catalyst surface.

Test

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