In a convergent-divergent (de Laval) nozzle for compressible flow, the pressure reaches minimum (maximum acceleration) at:

The correct answer is B: Throat (minimum area section). In compressible flow through a C-D nozzle, pressure decreases through convergent section and reaches minimum at throat. This is where velocity is maximum and Mach number = 1 (sonic condition).

The penetration theory for mass transfer assumes that:

The correct answer is A: Eddies expose fresh bulk fluid to the interface for short contact times. Penetration theory (Higbie) assumes eddies contact interface, remain for time θ, then submerge. More realistic than film theory for turbulent systems.

Which of the following best describes the boundary layer separation phenomenon?

The correct answer is B: Results from adverse pressure gradient causing flow reversal. Boundary layer separation occurs when an adverse (positive) pressure gradient opposes the flow, causing the flow to reverse near the wall and separate from the surface.

Which of the following materials would be most suitable for a heat sink application requiring high thermal conductivity and low cost?

The correct answer is B: Aluminum alloy (k = 160 W/m·K). Aluminum alloys offer an excellent balance of thermal conductivity (160 W/m·K, sufficient for most applications), cost-effectiveness, light weight, corrosion resistance, and ease of machining. While copper has higher conductivity, aluminum's cost-benefit ratio is superior for heat sink applications.

The entropy change for an isothermal irreversible expansion of an ideal gas from V₁ to V₂ is:

The correct answer is A: ΔS = nR ln(V₂/V₁). For an isothermal process of ideal gas, entropy depends only on volume ratio: ΔS = nR ln(V₂/V₁), regardless of reversibility

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Chemical Engineering

Process design, thermodynamics, reactions

117 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 21–30 of 117

Topics in Chemical Engineering

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

Q.21 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.22 Hard Chemical Reaction Engineering

In consecutive reactions A → B → C (both first-order), maximum concentration of intermediate B occurs at which time?

A t = ln(k₂/k₁)/(k₂-k₁)

B t = ln(k₁/k₂)/(k₁-k₂)

C t = 1/k₁ + 1/k₂

D t = k₁ × k₂

Correct Answer: B. t = ln(k₁/k₂)/(k₁-k₂)

EXPLANATION

Maximum [B] occurs when d[B]/dt = 0, giving t_max = ln(k₁/k₂)/(k₁-k₂) for k₁ ≠ k₂.

Test

Q.23 Hard Chemical Reaction Engineering

For a polymerization reaction in a batch reactor, the polydispersity index (PDI) and average molecular weight depend on:

A Only the initiation rate

B The ratio of propagation to termination rate constants and conversion

C Temperature alone

D The reactor volume

Correct Answer: B. The ratio of propagation to termination rate constants and conversion

EXPLANATION

PDI and molecular weight distribution in batch polymerization depend on the relative magnitudes of propagation and termination reactions and the degree of conversion achieved.

Test

Q.24 Hard Chemical Reaction Engineering

In the design of a CSTR for a reaction with Arrhenius parameters: Ea = 50 kJ/mol, A = 10⁵ s⁻¹, what is the approximate k at 50°C?

A 2.3 × 10³ s⁻¹

B 1.8 × 10² s⁻¹

C 4.2 × 10⁴ s⁻¹

D 6.7 × 10³ s⁻¹

Correct Answer: C. 4.2 × 10⁴ s⁻¹

EXPLANATION

k = A·exp(-Ea/RT) = 10⁵·exp(-50000/(8.314×323)) = 10⁵·exp(-1.86) ≈ 10⁵ × 0.156 ≈ 1.56 × 10⁴ s⁻¹. Closest is option C.

Test

Q.25 Hard Chemical Reaction Engineering

For parallel reactions where A → B (desired) with rate constant k₁ and A → C (undesired) with rate constant k₂, the selectivity towards B is maximized by:

A Increasing temperature if Ea1 > Ea2

B Using a CSTR regardless of kinetic parameters

C Minimizing concentration of A if reaction order in A differs

D Using a PFR with low inlet concentration

Correct Answer: A. Increasing temperature if Ea1 > Ea2

EXPLANATION

If Ea1 > Ea2, increasing temperature favors the desired reaction with higher activation energy, improving selectivity to B.

Test

Q.26 Hard Chemical Reaction Engineering

The Weisz-Prater criterion is used to determine:

A Whether internal mass transfer limitations exist in catalytic reactions

B The optimal catalyst particle size

C The heat transfer coefficient in a reactor

D The reaction order from experimental data

Correct Answer: A. Whether internal mass transfer limitations exist in catalytic reactions

EXPLANATION

Weisz-Prater number: CWP = (k''ρcRp²)/De. If CWP << 0.15, internal diffusion limitations are negligible.

Test

Q.27 Hard Chemical Reaction Engineering

For a second-order reaction in a PFR, increasing the inlet concentration while maintaining constant volumetric flow rate will result in:

A Decreased conversion

B Increased absolute reaction rate but decreased conversion

C Unchanged conversion (conversion is independent of inlet concentration)

D Proportional increase in both reaction rate and conversion

Correct Answer: C. Unchanged conversion (conversion is independent of inlet concentration)

EXPLANATION

In a PFR, conversion (fractional) depends on space-time and reaction kinetics but is independent of inlet concentration for a given residence time.

Test

Q.28 Hard Chemical Reaction Engineering

Which reactor configuration minimizes backmixing while maintaining high mass transfer rates for liquid-liquid reactions between immiscible phases?

A Stirred tank reactor with baffles

B Microfluidic segmented flow reactor

C Trickle bed reactor

D Oscillatory baffled reactor

Correct Answer: B. Microfluidic segmented flow reactor

EXPLANATION

Microfluidic segmented flow reactors provide plug-flow characteristics with enhanced interfacial area and mass transfer through controlled droplet generation in immiscible phases.

Test

Q.29 Hard Chemical Reaction Engineering

In cascade impaction for studying particle-phase reaction kinetics in reactors, which aerodynamic diameter range represents particles most suitable for chemical reaction on catalyst surfaces?

A 0.01-0.1 μm

B 0.5-5 μm

C 10-100 μm

D >100 μm

Correct Answer: B. 0.5-5 μm

EXPLANATION

Particles in 0.5-5 μm range offer optimal surface area for catalytic reactions while maintaining reasonable diffusivity and reactivity characteristics.

Test

Q.30 Hard Chemical Reaction Engineering

For a gas-phase reaction in a fluidized bed reactor, the overall reaction rate is limited by mass transfer from bulk to catalyst surface. Which step shows zero-order kinetics behavior?

A Chemical reaction on catalyst surface

B External mass transfer to catalyst

C Internal pore diffusion

D Adsorption of reactants

Correct Answer: B. External mass transfer to catalyst

EXPLANATION

When external mass transfer is rate-limiting, the flux is proportional to concentration difference with fixed mass transfer coefficient, resulting in zero-order kinetics with respect to bulk concentration.

Test

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