In a settling tank (clarifier) with depth H = 2 m, overflow rate = 1 m³/m²·h, and settling velocity of particles = 0.02 m/min, will the particles settle completely?

The correct answer is A: Yes, settling velocity is much higher. Settling velocity = 0.02 m/min = 1.2 m/h. Overflow rate = 1 m³/m²·h means rise velocity = 1 m/h < 1.2 m/h, so particles will settle

For a dilute binary gas mixture diffusing through a stagnant layer, the diffusion coefficient D_AB can be estimated using the Chapman-Enskog theory. Which statement is correct?

The correct answer is B: D_AB is inversely proportional to pressure. According to Chapman-Enskog theory, D_AB ∝ T^(3/2)/P for gases. Thus, D_AB is inversely proportional to pressure at constant temperature.

A system absorbs 500 J of heat and does 300 J of work. The change in internal energy is:

The correct answer is A: 200 J. First law: ΔU = Q - W = 500 - 300 = 200 J (using convention W = work by system).

What does the selectivity parameter in a competing reaction system measure?

The correct answer is B: The ratio of desired product to undesired product formation rates. Selectivity S = rate of desired product formation / rate of undesired product formation, used to optimize reactor conditions for maximum desired product yield

A gas flows through a convergent nozzle. At what condition does maximum mass flow rate occur in the nozzle exit?

The correct answer is B: When Mach number at exit = 1.0 (sonic condition). For convergent nozzles, mass flow becomes independent of downstream pressure when throat reaches sonic conditions (M = 1)

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Chemical Engineering

Process design, thermodynamics, reactions

247 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 51–60 of 247

Topics in Chemical Engineering

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

Q.51 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.52 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.53 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.54 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.55 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.56 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.57 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.58 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.59 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

Q.60 Medium Chemical Reaction Engineering

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

A Surface reaction

B Internal diffusion

C External mass transfer

D Product desorption

Correct Answer: C. External mass transfer

EXPLANATION

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.

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