Which reactor configuration would be best suited for a fast, highly exothermic reaction where precise temperature control is critical?

The correct answer is B: Semi-batch reactor with one reactant fed slowly. Semi-batch allows controlled feeding of reactants, limiting instantaneous heat generation while maintaining good mixing and temperature control.

For a pseudosteady-state diffusion with heterogeneous reaction, the effectiveness factor η accounts for:

The correct answer is A: The reduction in reaction rate due to limited diffusion to active sites. η = (actual reaction rate)/(rate if all surface at bulk concentration). Important in catalytic reactors where diffusion and reaction compete.

Which reactor configuration gives maximum yield for a series reaction A→B→C where k₁ >> k₂?

The correct answer is A: Batch reactor with optimized residence time. For A→B→C series, batch allows control of residence time to maximize intermediate B before it converts to C

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

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Chemical Engineering
Mass Transfer

Process design, thermodynamics, reactions

46 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 21–30 of 46

Topics in Chemical Engineering

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

Q.21 Medium Mass Transfer

The concept of 'equivalent theoretical stages' in absorption is based on:

A Comparing actual performance with theoretical maximum from equilibrium stages

B Counting the number of stages physically present

C Calculating residence time in the column

D Measuring pressure drop across stages

Correct Answer: A. Comparing actual performance with theoretical maximum from equilibrium stages

EXPLANATION

Used to compare different types of contactors. Actual stages divided by Murphree efficiency gives equivalent theoretical stages needed.

Test

Q.22 Medium Mass Transfer

For gas absorption in a plate column, the gas-phase mass transfer coefficient increases with:

A Higher gas velocity and lower pressure

B Lower gas velocity and higher pressure

C Decreased column diameter

D Increased liquid viscosity

Correct Answer: A. Higher gas velocity and lower pressure

EXPLANATION

Higher velocity increases turbulence (higher k); lower pressure increases diffusivity D. Both increase Sh = kL/D.

Test

Q.23 Medium Mass Transfer

In distillation, the Murphree plate efficiency is defined as the ratio of:

A Actual separation achieved to theoretical maximum separation possible

B Vapor flow rate to liquid flow rate

C Stage temperature to feed temperature

D Condenser duty to reboiler duty

Correct Answer: A. Actual separation achieved to theoretical maximum separation possible

EXPLANATION

E_mv = (y_n - y_(n-1))/(y*_n - y_(n-1)), where y* is equilibrium vapor composition. Accounts for non-equilibrium stage behavior.

Test

Q.24 Medium Mass Transfer

For simultaneous heat and mass transfer in a cooling tower, the Lewis number (Le = α/D) typically has a value of:

A Approximately 1 for air-water system

B Always greater than 1

C Dependent only on temperature

D Independent of substance pair

Correct Answer: A. Approximately 1 for air-water system

EXPLANATION

For air-water system: Le = α/D ≈ 0.8-1.0. This means heat and mass transfer coefficients are comparable, important for cooling tower design.

Test

Q.25 Medium Mass Transfer

The penetration theory for mass transfer assumes that:

A Eddies expose fresh bulk fluid to the interface for short contact times

B A stagnant film exists at the interface indefinitely

C Mass transfer is independent of time

D Turbulence is completely absent

Correct Answer: A. Eddies expose fresh bulk fluid to the interface for short contact times

EXPLANATION

Penetration theory (Higbie) assumes eddies contact interface, remain for time θ, then submerge. More realistic than film theory for turbulent systems.

Test

Q.26 Medium Mass Transfer

In a continuous contacting device, the operating line is obtained from which fundamental principle?

A Material balance equation

B Energy balance

C Equilibrium relation

D Rate equation

Correct Answer: A. Material balance equation

EXPLANATION

Operating line represents all possible compositions entering and leaving the device based on material balance: Y₁ - Y₂ = (L/V)(X₁ - X₂)

Test

Q.27 Medium Mass Transfer

The Sherwood number (Sh) in mass transfer is analogous to which number in heat transfer?

A Nusselt number (Nu)

B Rayleigh number (Ra)

C Grashof number (Gr)

D Fourier number (Fo)

Correct Answer: A. Nusselt number (Nu)

EXPLANATION

Sh = kL·L/D is analogous to Nu = h·L/k. Both represent dimensionless transfer coefficients for mass and heat respectively.

Test

Q.28 Medium Mass Transfer

In a packed column absorption operation, the overall mass transfer coefficient KG is related to individual phase coefficients by:

A 1/KG = 1/kG + (m/kL)

B KG = kG + kL

C 1/KG = 1/kL + 1/kG

D KG = m·kG·kL

Correct Answer: A. 1/KG = 1/kG + (m/kL)

EXPLANATION

For gas-phase controlling resistance: 1/KG = 1/kG + (m/kL), where m is Henry's Law constant and accounts for equilibrium relationship.

Test

Q.29 Medium Mass Transfer

In the design of a sieve tray distillation column, the mass transfer efficiency (Murphree efficiency) accounts for:

A The deviation from equilibrium due to finite mass transfer rate

B The pressure drop across the tray

C The temperature gradient in the column

D The liquid holdup on the tray

Correct Answer: A. The deviation from equilibrium due to finite mass transfer rate

EXPLANATION

Murphree efficiency (E_M) reflects that equilibrium is not achieved on real trays due to limited contact time and finite mass transfer rates in the actual column.

Test

Q.30 Medium Mass Transfer

A spray tower is used for absorption where droplets fall through a rising gas stream. The interfacial area in such a system primarily depends on:

A Droplet size and number of droplets

B Tower height only

C Gas flow rate only

D Pressure and temperature

Correct Answer: A. Droplet size and number of droplets

EXPLANATION

Interfacial area 'a' in spray towers is directly proportional to the total surface area of droplets, which depends on droplet size (smaller droplets = larger area) and droplet density.

Test

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