In a jacketed CSTR for an endothermic reaction, increasing the heat transfer area per unit volume of reactor primarily affects which parameter?

The correct answer is C: Reaction rate and operating temperature stability. Increased heat transfer area improves heat supply rate for endothermic reactions, allowing higher operating temperatures with better temperature control and stability.

For an ideal gas undergoing adiabatic compression, the entropy change is:

The correct answer is C: Zero. For a reversible adiabatic process, dq = 0, therefore ΔS = ∫dq_rev/T = 0. Entropy remains constant during reversible adiabatic processes.

A gas flows through a convergent nozzle. At what condition does maximum mass flow rate occur in the nozzle exit?

The correct answer is B: When Mach number at exit = 1.0 (sonic condition). For convergent nozzles, mass flow becomes independent of downstream pressure when throat reaches sonic conditions (M = 1)

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:

The correct answer is B: 50 kmol/(s·atm). 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).

The mean residence time in a reactor can be calculated from RTD data using:

The correct answer is D: Both A and C are correct. Both equations are valid: the integral formulation and the volumetric flow definition give the same mean residence time.

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Chemical Engineering
Chemical Reaction Engineering

Process design, thermodynamics, reactions

51 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 31–40 of 51

Topics in Chemical Engineering

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

Q.31 Medium Chemical Reaction Engineering

What is the primary advantage of using a plug flow reactor (PFR) over a continuous stirred tank reactor (CSTR) for reactions with activation energy greater than 50 kJ/mol?

A Lower operating temperature requirements

B Better temperature control and safety

C Higher conversion at same residence time due to increasing temperature profile with reaction progress

D Lower capital and operating costs

Correct Answer: C. Higher conversion at same residence time due to increasing temperature profile with reaction progress

EXPLANATION

For high activation energy reactions, the increasing temperature from adiabatic exothermic reactions in PFR increases reaction rate progressively, improving conversion over CSTR where temperature is uniform and lower.

Test

Q.32 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.33 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.34 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.35 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.36 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.37 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.38 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.39 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.40 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

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