A cyclic heat engine operates between hot reservoir at 500 K and cold reservoir at 300 K. Maximum theoretical efficiency is:

The correct answer is B: 40%. Maximum efficiency is Carnot efficiency: η_max = 1 - T_cold/T_hot = 1 - 300/500 = 0.40 = 40%. No heat engine can exceed this efficiency.

For a reaction A + B → C where both reactants are supplied in stoichiometric ratio, if reaction order with respect to A is 1 and B is 1, and initial concentrations are each 2 mol/L, the integrated rate law shows conversion X varies as:

The correct answer is A: X increases linearly with time. For second-order reactions with equal initial concentrations CA0 = CB0, the integrated form simplifies to: CA = CA0/(1+kCA0×t), leading to pseudo-first order kinetics behavior

In equimolar counter-diffusion between two gases A and B, what is the relationship between their molar fluxes?

The correct answer is A: N_A = -N_B. In equimolar counter-diffusion, the molar fluxes of the two components are equal in magnitude but opposite in direction, hence N_A = -N_B.

In the Bernoulli equation, which term represents the pressure energy per unit volume?

The correct answer is C: P. The Bernoulli equation is P + ½ρV² + ρgz = constant. P itself is pressure energy per unit volume (not P/ρ which is pressure head).

The partial molar Gibbs energy at infinite dilution gives the chemical potential μ. For a component in ideal solution:

The correct answer is A: μᵢ = μᵢ⁰ + RT ln(xᵢ). For ideal solutions, the chemical potential is μᵢ = μᵢ⁰ + RT ln(xᵢ), where xᵢ is the mole fraction. For non-ideal solutions, the activity aᵢ = γᵢxᵢ is used.

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Chemical Engineering
Mass Transfer

Process design, thermodynamics, reactions

46 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 41–46 of 46

Topics in Chemical Engineering

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

Q.41 Medium Mass Transfer

What is the primary assumption made in the penetration theory of mass transfer?

A A stagnant film exists at the interface with linear concentration profile

B Fluid elements are exposed to the interface for a finite contact time, with unsteady diffusion

C Mass transfer occurs only at the stagnation points

D Concentration gradient is infinite at the interface

Correct Answer: B. Fluid elements are exposed to the interface for a finite contact time, with unsteady diffusion

EXPLANATION

Penetration theory (Higbie) assumes that fluid elements reach the interface, remain for a contact time θ, and then leave, with transient diffusion occurring during exposure.

Test

Q.42 Medium Mass Transfer

In a counter-current liquid-liquid extraction process, the extraction becomes more efficient when the difference between equilibrium and operating lines increases. What does this signify?

A Decreased interfacial area

B Increased driving force for mass transfer

C Higher system pressure

D Lower temperature operation

Correct Answer: B. Increased driving force for mass transfer

EXPLANATION

A larger gap between the operating line and equilibrium line indicates greater concentration difference, which increases the driving force (ΔC) for mass transfer, leading to higher transfer rates.

Test

Q.43 Medium Mass Transfer

The Sherwood number (Sh) correlates with Reynolds (Re) and Schmidt (Sc) numbers. For flow over a flat plate in laminar regime, which expression is approximately correct?

A Sh = 0.664 Re^(0.5) Sc^(1/3)

B Sh = 0.037 Re^(0.8) Sc^(1/3)

C Sh = Re × Sc

D Sh = (Re + Sc)/2

Correct Answer: A. Sh = 0.664 Re^(0.5) Sc^(1/3)

EXPLANATION

For laminar flow over a flat plate, the Chilton-Colburn analogy gives Sh = 0.664 Re^0.5 Sc^(1/3), analogous to the Nusselt number in heat transfer.

Test

Q.44 Medium Mass Transfer

A packed column is being used for absorption of SO₂ from air using water. The overall mass transfer coefficient K_L is related to individual coefficients by which relation?

A 1/K_L = 1/k_L + H/k_G

B 1/K_L = 1/k_L + 1/k_G

C K_L = k_L + k_G

D K_L = (k_L × k_G)/(k_L + k_G)

Correct Answer: A. 1/K_L = 1/k_L + H/k_G

EXPLANATION

For gas absorption with equilibrium relation y = Hx, the overall liquid phase coefficient is 1/K_L = 1/k_L + H/k_G, where H is Henry's law constant.

Test

Q.45 Medium Mass Transfer

In a distillation column operating at steady state, the mass transfer rate is governed by which of the following equations?

A N_A = k_L(C_A - C_AL)

B N_A = D_AB × (dC/dx)

C N_A = k_G(P_A - P_AL)

D All of the above are valid representations

Correct Answer: D. All of the above are valid representations

EXPLANATION

All three equations represent valid forms of mass transfer rate equations. Option A uses liquid phase coefficient, Option B is Fick's law, Option C uses gas phase coefficient, and all are interconnected through film theory.

Test

Q.46 Medium Mass Transfer

The relationship between mass transfer coefficient and diffusivity is given by the Chilton-Colburn analogy. If diffusivity doubles while other conditions remain constant, how does the mass transfer coefficient change (assuming laminar flow)?

A Increases by √2 times

B Increases by 2 times

C Increases by 2^(2/3) times

D Remains unchanged

Correct Answer: A. Increases by √2 times

EXPLANATION

In laminar flow, k ∝ D^(1/2). Therefore, if D doubles, k increases by √2 times (approximately 1.414 times).

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