In enzyme catalysis, what does the Michaelis-Menten constant (K_m) represent?

The correct answer is A: Substrate concentration at half maximum velocity. K_m represents substrate concentration [S] at which reaction velocity = V_max/2

The effectiveness-NTU (Number of Transfer Units) method is preferred over LMTD method when designing heat exchangers because:

The correct answer is B: LMTD method cannot handle cases where outlet temperatures are unknown (design problems). In heat exchanger design, outlet temperatures are unknown, making the LMTD method iterative and cumbersome. The NTU method (ε-NTU) directly uses inlet temperatures and known parameters to find the outlet temperatures without iteration, making it ideal for design problems.

In fluid mechanics, which dimensionless number represents the ratio of inertial forces to viscous forces?

The correct answer is A: Reynolds number. Reynolds number Re = (Inertial forces)/(Viscous forces) = ρVD/μ. It characterizes flow regime (laminar vs turbulent).

For an exothermic reaction in an adiabatic reactor, what happens to the reaction rate as conversion increases?

The correct answer is C: Increases due to temperature rise. Adiabatic reactor: no heat removal; exothermic reaction raises temperature, increasing k and hence rate

What is the order of reaction if the half-life period is independent of initial concentration?

The correct answer is B: First order. For first-order reactions, t₁/₂ = 0.693/k, which is independent of initial concentration C₀.

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Chemical Engineering
Mass Transfer

Process design, thermodynamics, reactions

32 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 21–30 of 32

Topics in Chemical Engineering

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

Q.21 Hard Mass Transfer

In ion exchange resins, the mass transfer resistance primarily occurs in:

A The particle pore structure (pore diffusion)

B The external liquid film

C The ion exchange reaction itself

D The resin backbone structure

Correct Answer: A. The particle pore structure (pore diffusion)

EXPLANATION

For ion exchange, intraparticle diffusion through pores is the rate-limiting step. External film resistance is negligible in comparison.

Test

Q.22 Hard Mass Transfer

For a binary gas mixture, the Stefan flow correction factor accounts for:

A Net molar flow due to unequal molar diffusion rates

B Pressure variations in the system

C Temperature gradients across the interface

D Viscosity changes with composition

Correct Answer: A. Net molar flow due to unequal molar diffusion rates

EXPLANATION

When one component condenses/reacts, equal molar counter-diffusion assumption breaks down. Stefan factor (B_m) corrects for net molar flow.

Test

Q.23 Hard Mass Transfer

For a hollow fiber membrane contactor used in gas-liquid mass transfer, the overall mass transfer coefficient K_OL is related to individual coefficients by:

A 1/K_OL = 1/k_G + m/k_L

B 1/K_OL = 1/k_L + 1/(m*k_G)

C K_OL = k_G + k_L

D K_OL = (k_G * k_L)/(k_G + k_L)

Correct Answer: B. 1/K_OL = 1/k_L + 1/(m*k_G)

EXPLANATION

For gas-liquid systems, 1/K_OL = 1/k_L + 1/(m*k_G), where m is the distribution coefficient. This accounts for both liquid and gas side resistances.

Test

Q.24 Hard Mass Transfer

For simultaneous momentum and mass transfer in a boundary layer, the Chilton-Colburn analogy relates j_D to friction factor f_D by:

A j_D = f_D / 2

B j_D = f_D

C j_D = 2 * f_D

D j_D = f_D * Sc^(1/3)

Correct Answer: A. j_D = f_D / 2

EXPLANATION

The Chilton-Colburn analogy states that j_D = j_H = f_D/2, assuming equivalent Pr and Sc values, relating mass transfer to friction factor.

Test

Q.25 Hard Mass Transfer

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?

A D_AB is independent of pressure

B D_AB is inversely proportional to pressure

C D_AB is directly proportional to pressure

D D_AB is independent of temperature

Correct Answer: B. D_AB is inversely proportional to pressure

EXPLANATION

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

Test

Q.26 Hard Mass Transfer

For a countercurrent liquid-liquid extraction process, the Kremser equation is used. What is the minimum number of stages required if the separation factor is 2.0 and the extraction factor is 1.5?

A Less than 3 stages

B Approximately 3-4 stages

C Approximately 5-6 stages

D Cannot be determined without additional information

Correct Answer: D. Cannot be determined without additional information

EXPLANATION

The Kremser equation requires initial and final solute concentrations or minimum separation requirements, which are not provided in the question.

Test

Q.27 Hard Mass Transfer

For a binary diffusion process, the flux equation according to Fick's law in terms of mole fractions is given by:

A N_A = -cD_AB(dc_A/dz) + y_A(N_A + N_B)

B N_A = cD_AB(dy_A/dz) + y_A(N_A + N_B)

C N_A = D_AB(dρ_A/dz)

D N_A = -D_AB(d²c_A/dz²)

Correct Answer: B. N_A = cD_AB(dy_A/dz) + y_A(N_A + N_B)

EXPLANATION

The molar flux equation in terms of mole fractions is N_A = cD_AB(dy_A/dz) + y_A(N_A + N_B), accounting for bulk flow effects.

Test

Q.28 Hard Mass Transfer

Which statement about the relationship between diffusivity and molar mass is correct according to kinetic theory?

A D_AB ∝ √(T/M_total)

B D_AB is independent of molar mass

C D_AB ∝ (M_A × M_B)^(1/2)

D D_AB is inversely proportional to molecular weight

Correct Answer: A. D_AB ∝ √(T/M_total)

EXPLANATION

From Chapman-Enskog theory, D_AB ∝ T^(3/2)/(P × σ²) × √(M_total), where D_AB is inversely related to molecular mass through the collision cross-section dependency.

Test

Q.29 Hard Mass Transfer

A bioprocess company needs to calculate oxygen transfer rate in an aerated bioreactor. The volumetric mass transfer coefficient k_L·a depends on which parameters?

A Superficial gas velocity and interfacial area per unit volume only

B Liquid properties (viscosity, surface tension), aeration rate, and impeller design

C Temperature and pressure only

D Oxygen partial pressure in inlet gas

Correct Answer: B. Liquid properties (viscosity, surface tension), aeration rate, and impeller design

EXPLANATION

k_L·a in bioreactors depends on fluid mechanics (impeller speed, gas flow rate), liquid properties affecting k_L, and equipment design affecting interfacial area 'a'. Temperature indirectly affects through viscosity changes.

Test

Q.30 Hard Mass Transfer

For simultaneous heat and mass transfer in a wet bulb thermometer, the Lewis number (Le) is defined as Le = Sc/Pr. If Le = 1, what can be inferred?

A Heat and mass transfer coefficients are equal

B Thermal diffusivity equals mass diffusivity

C Both a and b are correct

D The system is at equilibrium

Correct Answer: C. Both a and b are correct

EXPLANATION

When Le = 1 (Sc/Pr = 1), both analogy relationships hold: α = D_AB and h/ρc_p = k_L, making heat and mass transfer coefficients proportionally equal.

Test

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