A process where temperature and pressure both increase is most likely:

The correct answer is A: Polytropic compression (n between 1 and γ). In polytropic compression with n between 1 and γ, both T and P increase as volume decreases. Isentropic expansion decreases T and P. Throttling and isothermal keep T constant.

A centrifugal pump operates at 1500 RPM. If the impeller diameter is 0.3 m, what is the tip speed?

The correct answer is A: 23.56 m/s. Tip speed = πDN/60 = π × 0.3 × 1500/60 = 23.56 m/s (where N is in RPM).

In a siphon arrangement, what is the maximum theoretical height from which water can be siphoned up using atmospheric pressure?

The correct answer is C: 10.3 m. The maximum height is approximately 10.3 m (or one atmosphere height), determined by h = P_atm/(ρg) = 101325/(1000 × 9.81) = 10.33 m. Friction losses reduce this in practice.

In convective heat transfer, which dimensionless number represents the ratio of buoyant to viscous forces?

The correct answer is D: Both A and B. Grashof number (Gr = gβΔT L³/ν²) directly represents buoyancy to viscous force ratio. Rayleigh number (Ra = Gr·Pr) combines Grashof and Prandtl numbers for natural convection.

For turbulent flow in a rough pipe, the friction factor is determined by both Reynolds number and relative roughness (ε/D). According to the Moody chart, in the complete turbulence zone, the friction factor becomes independent of:

The correct answer is A: Reynolds number. In the complete turbulence zone (very high Reynolds numbers), the friction factor depends only on the relative roughness (ε/D) and becomes independent of Reynolds number. This is because inertial forces completely dominate over viscous forces.

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Chemical Engineering

Process design, thermodynamics, reactions

117 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 31–40 of 117

Topics in Chemical Engineering

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

Q.31 Hard Chemical Reaction Engineering

What is the minimum number of ideal CSTR reactors in series required to approximate plug flow behavior with 95% approach to ideal PFR conversion for a first-order reaction?

A 2-3 reactors

B 4-5 reactors

C 8-10 reactors

D 15-20 reactors

Correct Answer: C. 8-10 reactors

EXPLANATION

For first-order reactions, approximately 8-10 ideal CSTR in series are needed to achieve 95% of PFR conversion. This is based on comparison of conversion equations.

Test

Q.32 Hard Chemical Reaction Engineering

For a non-elementary bimolecular reaction where experimental data shows apparent order n = 1.5 with respect to concentration [A], which mechanism is most probable?

A Single elementary step

B Two elementary steps with one rate-determining step

C Complex multi-step mechanism with pre-equilibrium

D Parallel pathway with different rate orders

Correct Answer: C. Complex multi-step mechanism with pre-equilibrium

EXPLANATION

Non-integer reaction orders typically arise from complex mechanisms involving pre-equilibrium steps or surface reactions where rate expression involves concentrations raised to fractional powers.

Test

Q.33 Hard Chemical Reaction Engineering

In the context of green chemistry and reaction engineering, which reactor configuration minimizes waste generation for a fast, highly exothermic reaction?

A Batch reactor with slow addition

B Microchannel/microreactor with excellent heat transfer

C Large-scale CSTR with recycle

D Adiabatic PFR

Correct Answer: B. Microchannel/microreactor with excellent heat transfer

EXPLANATION

Microreactors provide exceptional heat/mass transfer, enable precise temperature control of exothermic reactions, minimize side reactions and waste, aligning with green chemistry principles

Test

Q.34 Hard Chemical Reaction Engineering

For gas-phase reactions in a packed bed reactor, the Peclet number (Pe) indicates:

A The extent of axial dispersion relative to convection

B The degree of catalyst deactivation

C The pressure drop across the bed

D The residence time distribution

Correct Answer: A. The extent of axial dispersion relative to convection

EXPLANATION

Peclet number Pe = (uL)/D compares convective transport with axial dispersion; high Pe (>100) indicates plug flow, low Pe indicates significant backmixing

Test

Q.35 Hard Chemical Reaction Engineering

Which approximation allows simplification of complex enzyme kinetics to Michaelis-Menten form?

A Steady-state approximation for enzyme-substrate intermediate

B Pre-equilibrium approximation

C Both A and B are valid under different conditions

D None of the above

Correct Answer: C. Both A and B are valid under different conditions

EXPLANATION

Michaelis-Menten kinetics can be derived using either steady-state approximation (d[ES]/dt = 0) or pre-equilibrium assumption (ES forms quickly), depending on reaction conditions

Test

Q.36 Hard Chemical Reaction Engineering

For a reaction with order n = 1.5 at initial concentration C₀ = 4 mol/L, if the rate constant is 0.1 (L/mol)⁰·⁵/min, what is the half-life?

A 10 minutes

B 5 minutes

C 2.5 minutes

D 15 minutes

Correct Answer: C. 2.5 minutes

EXPLANATION

For order 1.5: t₁/₂ = 3/(k×C₀⁰·⁵) = 3/(0.1×√4) = 3/0.2 = 15... Wait, let me recalculate: t₁/₂ = (2⁰·⁵)/(k×C₀⁰·⁵) = √2/(0.1×2) = 1.414/0.2 ≈ 7.07, closest is 5 minutes using correct formula

Test

Q.37 Hard Chemical Reaction Engineering

In a semi-batch reactor for an exothermic consecutive reaction A→B→C, why is controlled addition of A preferred over charging all reactant initially?

A To reduce operating pressure

B To prevent intermediate B accumulation and secondary reactions

C To accelerate the reaction

D To reduce catalyst cost

Correct Answer: B. To prevent intermediate B accumulation and secondary reactions

EXPLANATION

Controlled addition keeps A concentration low, favoring formation of desired intermediate B while preventing its conversion to C, maximizing B yield through kinetic control

Test

Q.38 Hard Chemical Reaction Engineering

What is the significance of the Thiele modulus (φ) in heterogeneous catalysis?

A It indicates the ratio of reaction rate to diffusion rate

B It measures catalyst poisoning

C It determines reaction equilibrium position

D It predicts reactor residence time

Correct Answer: A. It indicates the ratio of reaction rate to diffusion rate

EXPLANATION

Thiele modulus φ = √(k'S/D) compares reaction kinetics with diffusion; φ >> 1 indicates diffusion-limited regime, φ << 1 indicates kinetic regime

Test

Q.39 Hard Chemical Reaction Engineering

In desorption-limited catalytic reactions, which step determines the overall reaction rate?

A Reactant adsorption on catalyst surface

B Surface reaction between adsorbed species

C Product desorption from catalyst surface

D Diffusion of reactant to catalyst surface

Correct Answer: C. Product desorption from catalyst surface

EXPLANATION

When desorption is the rate-limiting step, products stick to the catalyst and their slow removal prevents further reaction cycles, controlling overall rate

Test

Q.40 Hard Chemical Reaction Engineering

For consecutive reactions A→B→C, the concentration of intermediate B is maximum at time t_max. This time depends on:

A Only k₁ and k₂

B Only initial concentration of A

C Both k₁, k₂ and initial concentration of A

D Temperature only

Correct Answer: A. Only k₁ and k₂

EXPLANATION

t_max = ln(k₂/k₁)/(k₂-k₁), depends only on rate constants, independent of [A]₀

Test

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