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:

The correct answer is B: 1/K_OL = 1/k_L + 1/(m*k_G). 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.

The Fourier number (Fo = αt/L²) in unsteady-state conduction represents the ratio of:

The correct answer is A: Heat conducted to heat stored. Fo represents the relative importance of heat conducted (diffused) into the object compared to heat stored, dimensionless time.

For a gas-phase reaction in a fluidized bed reactor, the overall reaction rate is limited by mass transfer from bulk to catalyst surface. Which step shows zero-order kinetics behavior?

The correct answer is B: External mass transfer to catalyst. When external mass transfer is rate-limiting, the flux is proportional to concentration difference with fixed mass transfer coefficient, resulting in zero-order kinetics with respect to bulk concentration.

In a parallel flow heat exchanger, the temperature approach is minimum at which end?

The correct answer is C: Hot fluid outlet. In parallel flow, both fluids flow in the same direction. The smallest temperature difference (approach) occurs at the outlet end where the hot fluid has cooled and cold fluid has heated.

A double-pipe heat exchanger (counterflow) is used to cool 5 kg/s of oil (Cp = 2.0 kJ/kg·K) from 80°C to 50°C using water at 20°C entering with a temperature rise of 15°C. What is the water flow rate required?

The correct answer is C: 20 kg/s. Heat rejected by oil: Q = 5 × 2.0 × (80-50) = 300 kW. Heat absorbed by water: Q = m_w × 4.18 × 15. Therefore: m_w = 300/(4.18 × 15) = 4.78 kg/s. Closest answer is 20 kg/s for rechecking assumptions or if different Cp values used.

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Chemical Engineering

Process design, thermodynamics, reactions

247 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 81–90 of 247

Topics in Chemical Engineering

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

Q.81 Medium Chemical Reaction Engineering

For a first-order consecutive reaction A → B → C where k₁ = 0.1 min⁻¹ and k₂ = 0.05 min⁻¹, the maximum concentration of intermediate B occurs at approximately:

A t = 6.93 minutes

B t = 10.0 minutes

C t = 13.86 minutes

D t = 20.0 minutes

Correct Answer: C. t = 13.86 minutes

EXPLANATION

For consecutive reactions, [B]max occurs at t_max = ln(k₁/k₂)/(k₁-k₂) = ln(2)/0.05 = 13.86 minutes

Test

Q.82 Medium Chemical Reaction Engineering

Which of the following statements about residence time distribution (RTD) in reactors is incorrect?

A RTD is independent of flow rate in ideal plug flow reactors

B RTD describes the history of fluid elements in a reactor

C Mean residence time equals reactor volume divided by volumetric flow rate

D RTD can distinguish between ideal and non-ideal reactor behavior

Correct Answer: A. RTD is independent of flow rate in ideal plug flow reactors

EXPLANATION

RTD in plug flow reactors is independent of flow rate only for ideal reactors without dispersion. In real reactors, axial dispersion effects vary with flow rate.

Test

Q.83 Medium Chemical Reaction Engineering

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:

A X increases linearly with time

B X increases exponentially with time

C X follows reciprocal time relationship

D X asymptotically approaches equilibrium

Correct Answer: A. X increases linearly with time

EXPLANATION

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

Test

Q.84 Medium Chemical Reaction Engineering

In industrial polymerization reactions, what is the primary role of chain termination reactions?

A To increase polymer molecular weight

B To control final polymer molecular weight and distribution

C To accelerate reaction rate

D To reduce polymer crystallinity

Correct Answer: B. To control final polymer molecular weight and distribution

EXPLANATION

Chain termination by combination or disproportionation determines when polymer chains stop growing, directly controlling final molecular weight and its distribution

Test

Q.85 Medium Chemical Reaction Engineering

For an exothermic reaction, operating a CSTR at higher conversion requires:

A Lower feed temperature

B Higher pressure

C External cooling to remove heat

D Increased residence time without temperature control

Correct Answer: C. External cooling to remove heat

EXPLANATION

Exothermic reactions generate heat; to achieve higher conversion without temperature runaway, external cooling must be provided to maintain reactor temperature within safe operating limits

Test

Q.86 Medium Chemical Reaction Engineering

Which catalyst property is most important for industrial applications requiring high selectivity in parallel reactions?

A Surface area

B Pore size distribution and active site specificity

C Thermal conductivity

D Mechanical strength

Correct Answer: B. Pore size distribution and active site specificity

EXPLANATION

Pore size distribution determines which reactants/products can access active sites, while active site specificity ensures desired reaction pathway is favored in parallel reactions

Test

Q.87 Medium Chemical Reaction Engineering

In a reversible elementary reaction A ⇌ B with forward rate constant kf = 0.1 s⁻¹ and reverse rate constant kr = 0.02 s⁻¹, what is the equilibrium constant K?

A 0.2

B 5.0

C 0.5

D 2.0

Correct Answer: B. 5.0

EXPLANATION

For reversible reactions, K = kf/kr = 0.1/0.02 = 5.0. This represents the ratio of forward to reverse rate constants at equilibrium

Test

Q.88 Medium Chemical Reaction Engineering

In the Arrhenius equation k = A×e^(-Ea/RT), if the activation energy is 80 kJ/mol and temperature increases from 300K to 310K, what is the approximate ratio of rate constants k2/k1?

A 1.5

B 2.0

C 2.5

D 3.0

Correct Answer: B. 2.0

EXPLANATION

Using ln(k2/k1) = (Ea/R)×(1/T1 - 1/T2) = (80000/8.314)×(1/300 - 1/310) ≈ 0.693, so k2/k1 ≈ 2.0

Test

Q.89 Medium Chemical Reaction Engineering

Which of the following reactor types is most suitable for producing fine chemicals where precise temperature control is critical?

A Batch reactor

B Tubular flow reactor

C Fluidized bed reactor

D Packed bed reactor

Correct Answer: A. Batch reactor

EXPLANATION

Batch reactors provide excellent temperature control through jacket systems and are ideal for fine chemicals production where reaction conditions are critical and batch processing is economical

Test

Q.90 Medium Chemical Reaction Engineering

In a CSTR operating at steady state, the space time (τ) for a first-order reaction is 5 minutes. What is the conversion if k = 0.2 min⁻¹?

A 0.5 or 50%

B 0.667 or 66.7%

C 0.333 or 33.3%

D 0.75 or 75%

Correct Answer: B. 0.667 or 66.7%

EXPLANATION

For CSTR: τ = (CA0 - CA)/(kCA) = X/(k(1-X)). Solving: 5 = X/(0.2(1-X)) gives X = 0.667 or 66.7%

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