The compressibility factor Z for a real gas at high pressure and low temperature typically shows:

The correct answer is B: Z < 1, indicating attractive forces dominate. At high P and low T, attractive intermolecular forces dominate over repulsion, making Z < 1. This indicates volume is less than ideal gas volume (PV < nRT).

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?

The correct answer is C: Complex multi-step mechanism with pre-equilibrium. 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.

In computational fluid dynamics (CFD), the Courant number (Co = U×Δt/Δx) is important for numerical stability. For explicit schemes, the Courant number should be:

The correct answer is A: Co ≤ 1. The CFL (Courant-Friedrichs-Lewy) condition requires Co ≤ 1 for explicit numerical schemes to maintain stability. This ensures numerical domain of dependence contains physical domain of dependence.

For an open system, the steady flow energy equation relates enthalpy rather than internal energy because:

The correct answer is B: It accounts for flow work (PV) at inlet and exit. H = U + PV. The PV term represents flow work needed to push fluid across system boundaries in steady flow

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Chemical Engineering

Process design, thermodynamics, reactions

247 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 211–220 of 247

Topics in Chemical Engineering

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

Q.211 Medium Mass Transfer

The height of a transfer unit (HTU) in a packed absorption column represents:

A The column height for one theoretical stage

B The height required for one unit of concentration change

C The effective height of packing material

D The bed expansion during operation

Correct Answer: B. The height required for one unit of concentration change

EXPLANATION

HTU = V·G/(k_G·a·A), where a smaller HTU indicates more efficient mass transfer. It represents the column height needed to achieve one logarithmic unit of concentration driving force reduction.

Test

Q.212 Medium Mass Transfer

A gas A diffuses through a stagnant film of gas B. If the diffusivity D_AB = 0.1 cm²/s, film thickness δ = 0.01 cm, and concentration difference = 0.05 mol/cm³, the diffusive flux is:

A 5 × 10⁻⁴ mol/(cm²·s)

B 5 × 10⁻³ mol/(cm²·s)

C 5 × 10⁻² mol/(cm²·s)

D 5 × 10⁻¹ mol/(cm²·s)

Correct Answer: B. 5 × 10⁻³ mol/(cm²·s)

EXPLANATION

Using Fick's law for stagnant diffusion: J = D_AB·ΔC/δ = 0.1 × 0.05 / 0.01 = 0.5 × 10⁻² = 5 × 10⁻³ mol/(cm²·s).

Test

Q.213 Medium Mass Transfer

In membrane separation, the permeate flux in reverse osmosis is given by:

A J = k_m(C_feed - C_permeate)

B J = A(ΔP - Δπ)

C J = (P - P_osmotic)/μ

D J = D·(C_feed/C_permeate)

Correct Answer: B. J = A(ΔP - Δπ)

EXPLANATION

The reverse osmosis permeate flux follows: J = A(ΔP - Δπ), where A is membrane permeability, ΔP is applied pressure, and Δπ is osmotic pressure difference.

Test

Q.214 Medium Mass Transfer

For absorption of a sparingly soluble gas in a liquid with fast reaction kinetics, the enhancement factor 'E' is determined by:

A Henry's law constant only

B Reaction rate constant and diffusivities of reactants

C Only the liquid-phase mass transfer coefficient

D Gas solubility and liquid viscosity

Correct Answer: B. Reaction rate constant and diffusivities of reactants

EXPLANATION

The enhancement factor E = k_L,with reaction/k_L,without reaction depends on the Hatta number (Ha = √(k·C_A0·D_A/k_L²)), which incorporates reaction kinetics and mass transfer parameters.

Test

Q.215 Medium Mass Transfer

The penetration theory for mass transfer assumes that the contact time between fluid elements is:

A Very long, allowing complete equilibration

B Very short, with exposure to a semi-infinite diffusion medium

C Moderate, following first-order kinetics

D Variable depending on turbulent intensity

Correct Answer: B. Very short, with exposure to a semi-infinite diffusion medium

EXPLANATION

Penetration theory assumes fluid elements contact the interface for a short time, then move away. Mass transfer is modeled using unsteady diffusion into a semi-infinite medium.

Test

Q.216 Medium Mass Transfer

In a countercurrent absorption column, if the gas-phase mass transfer coefficient is k_G = 0.05 kmol/(m²·s·atm), the interfacial area 'a' = 200 m²/m³, and column cross-section = 5 m², the volumetric overall mass transfer coefficient is:

A 10 kmol/(s·atm)

B 50 kmol/(s·atm)

C 500 kmol/(s·atm)

D 5 kmol/(s·atm)

Correct Answer: B. 50 kmol/(s·atm)

EXPLANATION

Overall volumetric mass transfer = k_G × a × Volume = 0.05 × 200 × (5 × height). For unit height, K_G·a·V = 0.05 × 200 × 5 = 50 kmol/(s·atm).

Test

Q.217 Medium Mass Transfer

The Stefan problem in mass transfer involves:

A Unsteady diffusion with a moving boundary

B Steady-state absorption in packed columns

C Diffusion through a stagnant film

D Turbulent mass transfer in pipes

Correct Answer: A. Unsteady diffusion with a moving boundary

EXPLANATION

The Stefan problem deals with unsteady diffusion with a moving interface, commonly encountered in evaporation from droplets and sublimation processes where the interface position changes with time.

Test

Q.218 Medium Mass Transfer

For equimolar counter-diffusion in a binary system, the molar fluxes satisfy:

A J_A = J_B

B J_A = -J_B

C J_A + J_B = 0

D Both B and C are correct

Correct Answer: D. Both B and C are correct

EXPLANATION

In equimolar counter-diffusion, moles of A diffusing in one direction equal moles of B diffusing in the opposite direction, making J_A = -J_B and their sum zero.

Test

Q.219 Medium Mass Transfer

The Fick's first law of diffusion in binary mixtures states that the molar flux J_A is proportional to:

A Concentration gradient only

B Concentration gradient and bulk flow

C Pressure gradient only

D Temperature gradient only

Correct Answer: B. Concentration gradient and bulk flow

EXPLANATION

Fick's law: J_A = -D_AB(dC_A/dz) + C_A(J_A + J_B). The total flux includes both diffusive and convective contributions due to bulk flow.

Test

Q.220 Medium Mass Transfer

In membrane separation processes, the selectivity is expressed as:

A Ratio of permeance of component A to component B

B The absolute flux of one component

C The pressure difference across membrane

D The membrane thickness

Correct Answer: A. Ratio of permeance of component A to component B

EXPLANATION

Selectivity α = (J_A/ΔP_A)/(J_B/ΔP_B). Higher selectivity indicates better separation capability of the membrane.

Test

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