In a heterogeneous catalytic reaction, the overall rate is limited by which step if the external mass transfer coefficient is very small?

The correct answer is C: External mass transfer. A very small external mass transfer coefficient creates a large resistance to diffusion from bulk to particle surface, making external mass transfer the rate-limiting step.

For a non-isothermal diffusion process with coupled heat and mass transfer, the Lewis number Le is defined as:

The correct answer is A: Ratio of thermal diffusivity to mass diffusivity. Lewis number Le = α/D_AB, where α is thermal diffusivity. It indicates the relative importance of heat and mass transfer in coupled processes. Le ≈ Sc/Pr for most gases.

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.

In a membrane separation process, the permeance of a membrane is defined as flux per unit driving force. What are the typical units of permeance in SI system?

The correct answer is A: mol/(m²·s·Pa). Permeance has units of mol/(m²·s·Pa) when flux is in mol/(m²·s) and driving force (pressure difference) is in Pa. It represents the ease of species permeation through the membrane.

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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 1–10 of 51

Topics in Chemical Engineering

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

Q.1 Medium Chemical Reaction Engineering

In a CSTR operating at steady state with a first-order irreversible reaction A → B, if the volumetric flow rate is doubled while keeping reactor volume constant, how does the conversion of reactant A change?

A Conversion increases because residence time increases

B Conversion decreases because residence time decreases

C Conversion remains unchanged as it depends only on rate constant

D Conversion doubles due to increased feed concentration

Correct Answer: B. Conversion decreases because residence time decreases

EXPLANATION

In a CSTR, conversion depends on residence time (τ = V/Q). When volumetric flow rate Q doubles while V remains constant, residence time τ decreases by half. Since conversion X_A = kτ/(1+kτ) for first-order reaction, decreased τ leads to decreased conversion. This is a fundamental principle in reactor design for 2024-25 competitive exams.

Test

Q.2 Medium Chemical Reaction Engineering

For a reaction with activation energy E_a = 50 kJ/mol, by what factor does rate constant increase if temperature increases from 300K to 310K? (R = 8.314 J/mol·K)

A 1.5

B 2.0

C 2.5

D 3.0

Correct Answer: B. 2.0

EXPLANATION

Using Arrhenius: ln(k₂/k₁) = (E_a/R)(T₂-T₁)/(T₁T₂) ≈ 1.96, so k₂/k₁ ≈ 2.0

Test

Q.3 Medium Chemical Reaction Engineering

For isothermal batch reactor with r = -dC_A/dt = kC_A^n, what is the integrated rate law for n=2?

A 1/C_A - 1/C_A0 = kt

B ln(C_A/C_A0) = -kt

C C_A = C_A0·exp(-kt)

D C_A - C_A0 = -kt

Correct Answer: A. 1/C_A - 1/C_A0 = kt

EXPLANATION

For second-order: ∫dC_A/C_A² = -k∫dt gives 1/C_A - 1/C_A0 = kt.

Test

Q.4 Medium Chemical Reaction Engineering

In microbial fermentation kinetics, the Monod equation models specific growth rate. What happens when substrate concentration >> K_s?

A Growth rate becomes zero-order with respect to substrate

B Growth rate becomes first-order with respect to substrate

C Growth rate becomes second-order

D Growth rate is independent of substrate

Correct Answer: A. Growth rate becomes zero-order with respect to substrate

EXPLANATION

When [S] >> K_s, μ ≈ μ_max, making growth zero-order in substrate (Monod equation simplification).

Test

Q.5 Medium Chemical Reaction Engineering

For competitive-consecutive reactions: A → B (k₁), A → C (k₂), B → D (k₃), selectivity of B over C is defined as S_B/C = ?

A k₁/k₂

B [B]/[C]

C k₁/k₂ × (1-exp(-k₃t))

D k₁/(k₁+k₂)

Correct Answer: A. k₁/k₂

EXPLANATION

For parallel reactions, instantaneous selectivity S_B/C = k₁/k₂, independent of time at low conversions.

Test

Q.6 Medium Chemical Reaction Engineering

In a reactor with catalyst deactivation following first-order decay, what is the effect on reactant conversion over time?

A Conversion increases

B Conversion decreases exponentially

C Conversion remains constant

D Conversion increases then plateaus

Correct Answer: B. Conversion decreases exponentially

EXPLANATION

Catalyst activity decays as a = exp(-k_d·t), causing effective rate constant to decrease, reducing conversion over time.

Test

Q.7 Medium Chemical Reaction Engineering

What does the Damköhler number (Da) represent in reactor design?

A Ratio of kinetic rate to diffusion rate

B Ratio of reaction rate to flow rate

C Ratio of reactor volume to feed rate

D Ratio of activation energy to thermal energy

Correct Answer: B. Ratio of reaction rate to flow rate

EXPLANATION

Da = reaction rate/flow rate, determining whether reaction or flow dominates; Da >> 1 means reaction-limited.

Test

Q.8 Medium Chemical Reaction Engineering

In a CSTR operating at steady state, if volumetric flow rate increases while keeping concentration constant, what happens to conversion?

A Increases

B Decreases

C Remains constant

D First increases then decreases

Correct Answer: B. Decreases

EXPLANATION

Increased flow rate reduces residence time τ = V/F. For CSTR, X = kτ/(1+kτ), so increased τ means decreased conversion.

Test

Q.9 Medium Chemical Reaction Engineering

Which reactor configuration provides the highest conversion for an endothermic reaction at equilibrium?

A Batch reactor

B CSTR

C PFR

D Membrane reactor with in-situ product removal

Correct Answer: D. Membrane reactor with in-situ product removal

EXPLANATION

Membrane reactors shift equilibrium by removing products, overcoming equilibrium limitations in endothermic reactions.

Test

Q.10 Medium Chemical Reaction Engineering

In a plug flow reactor (PFR), what is the relationship between conversion and reactor volume for a first-order reaction?

A Conversion increases linearly with volume

B Conversion increases exponentially with volume

C Conversion is independent of volume

D Conversion decreases with increasing volume

Correct Answer: B. Conversion increases exponentially with volume

EXPLANATION

For a first-order reaction in PFR, X = 1 - exp(-kτ), showing exponential relationship with residence time and thus volume.

Test

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