In the context of reaction kinetics, which statement best describes the rate-determining step (RDS) in a multi-step reaction mechanism?

The correct answer is B: It is the slowest step that controls the overall reaction rate. The rate-determining step is the slowest elementary step in the reaction mechanism, which governs the overall rate of the reaction regardless of its position in the sequence

In reverse osmosis (RO), the membrane flux equation (Darcy's law for membranes) predicts that flux is:

The correct answer is D: Both B and C are correct. RO flux J = (k_m/μ)·ΔP/Δx, where flux is directly proportional to pressure difference and inversely to membrane thickness, following modified Darcy's equation.

In the 2024-2025 update to heat exchanger design standards (TEMA), which of the following represents the most significant advancement in fouling prediction for industrial heat exchangers?

The correct answer is A: Machine learning-based fouling models using operational data analytics. Recent advancements in heat exchanger design include AI/ML-based predictive fouling models that analyze operational data, surface properties, and fluid characteristics to provide dynamic fouling resistance predictions, replacing traditional static models for improved accuracy.

When CO₂ gas at 1 atm is cooled below the sublimation temperature (~195 K), it directly converts to dry ice without passing through liquid phase. This phenomenon is explained by:

The correct answer is A: Triple point pressure of CO₂ (5.1 atm) being higher than 1 atm. CO₂ triple point is at 5.1 atm and 216.6 K. At 1 atm, cooling solid CO₂ cannot reach liquid phase because pressure is insufficient. Sublimation occurs directly solid→gas.

In a finned tube heat exchanger, the overall surface effectiveness is 0.75. This means:

The correct answer is A: 75% of the theoretical maximum heat transfer is achieved. Overall surface effectiveness accounts for both fin and base surface contributions. A value of 0.75 indicates that 75% of the theoretical maximum heat transfer (assuming entire surface at base temperature) is actually achieved due to fin efficiency and geometric factors.

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Chemical Engineering
Chemical Reaction Engineering

Process design, thermodynamics, reactions

100 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 100

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 Hard Chemical Reaction Engineering

For homogeneous gas-phase reaction in batch reactor, if pressure increases at constant volume, what happens to reaction rate for 2A → Products?

A Decreases

B Remains unchanged

C Increases by factor of 4

D Increases by factor of 2

Correct Answer: C. Increases by factor of 4

EXPLANATION

Pressure increase increases concentration proportionally; for 2nd order rate = kC_A², quadrupling concentration increases rate 16-fold; doubling pressure quadruples rate.

Test

Q.3 Hard Chemical Reaction Engineering

In a recycle reactor with recycle ratio R, what is the volume reduction factor compared to PFR for equivalent conversion?

A (1+R)/R

B R/(1+R)

C (1+R)/(1+R²)

D 1 + 1/R

Correct Answer: A. (1+R)/R

EXPLANATION

Recycle reduces required volume by factor (1+R)/R compared to PFR for same conversion and residence time.

Test

Q.4 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.5 Easy Chemical Reaction Engineering

In CSTR, if inlet concentration C_A0 = 2 M, outlet concentration C_A = 0.5 M, what is fractional conversion?

A 0.25

B 0.5

C 0.75

D 1.0

Correct Answer: C. 0.75

EXPLANATION

Conversion X = (C_A0 - C_A)/C_A0 = (2 - 0.5)/2 = 0.75 or 75%.

Test

Q.6 Hard Chemical Reaction Engineering

Thiele modulus (φ) represents the ratio of which two parameters in heterogeneous catalysis?

A Reaction rate to diffusion rate

B Internal diffusion to surface reaction

C Kinetic rate constant to mass transfer coefficient

D Pore diameter to particle radius

Correct Answer: B. Internal diffusion to surface reaction

EXPLANATION

Thiele modulus φ = √(k·ρ_cat·a_s/D_eff) represents ratio of internal diffusion to surface reaction rate.

Test

Q.7 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.8 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.9 Easy Chemical Reaction Engineering

What is the space-time (τ) in a PFR if reactor volume is 100 L and volumetric feed rate is 10 L/min?

A 0.1 min

B 1 min

C 10 min

D 100 min

Correct Answer: C. 10 min

EXPLANATION

Space-time τ = V/v₀ = 100/10 = 10 min.

Test

Q.10 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

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