Which of the following statements about residence time distribution (RTD) in reactors is incorrect?
Answer: A
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.
Q.42Medium
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:
Answer: C
For consecutive reactions, [B]max occurs at t_max = ln(k₁/k₂)/(k₁-k₂) = ln(2)/0.05 = 13.86 minutes
Q.43Medium
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?
Answer: C
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.
Q.44Medium
In the Langmuir-Hinshelwood mechanism for catalytic reactions, what does the parameter K represent in the rate equation r = kK[A]/[1 + K[A]]?
Answer: A
In Langmuir-Hinshelwood kinetics, K is the equilibrium adsorption constant (K_ads) representing the balance between adsorption and desorption on catalyst surface.
Q.45Easy
For a reversible reaction A ⇌ B with forward rate constant k_f = 0.3 s⁻¹ and reverse rate constant k_r = 0.1 s⁻¹, what is the equilibrium constant K_c?
Answer: B
At equilibrium, K_c = k_f/k_r = 0.03.1 = 3.0. This represents the ratio of forward to reverse rate constants at equilibrium.
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Q.46Medium
In industrial practice, which method is most effective for controlling selectivity toward desired product in competitive parallel reactions?
Answer: C
For parallel reactions with different orders, maintaining low concentrations of reactants involved in undesired paths (particularly for higher-order undesired reactions) improves selectivity toward desired product.
Q.47Medium
The autocatalytic reaction A + B → 2B (where B is catalyst) exhibits which characteristic behavior?
Answer: B
Autocatalytic reactions show sigmoidal concentration-time curves due to product-catalyzed acceleration followed by deceleration as reactant concentration decreases.
Q.48Hard
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?
Answer: C
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.
Q.49Medium
In a fed-batch reactor for ester synthesis, maintaining the molar ratio of reactants at a specific value improves conversion. This strategy is known as:
Answer: B
Semi-batch reactors where one reactant is added gradually while maintaining optimal molar ratio with other reactants improve selectivity and conversion, especially for reversible reactions.
Q.50Hard
What is the minimum number of ideal CSTR reactors in series required to approximate plug flow behavior with 95% approach to ideal PFR conversion for a first-order reaction?
Answer: C
For first-order reactions, approximately 8-10 ideal CSTR in series are needed to achieve 95% of PFR conversion. This is based on comparison of conversion equations.
Q.51Medium
In the design of a photocatalytic reactor for degradation of pollutants, which parameter has the most significant effect on reaction rate?
Answer: B
Photocatalytic reactions fundamentally depend on photon absorption by the catalyst. Light intensity and wavelength matching the bandgap energy are critical for generating electron-hole pairs.
Q.52Hard
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?
Answer: B
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.
Q.53Medium
In a jacketed CSTR for an endothermic reaction, increasing the heat transfer area per unit volume of reactor primarily affects which parameter?
Answer: C
Increased heat transfer area improves heat supply rate for endothermic reactions, allowing higher operating temperatures with better temperature control and stability.
Q.54Medium
Which of the following best describes the role of the Damköhler number (Da) in reactor design?
Answer: B
The Damköhler number Da = k·τ (reaction rate constant × residence time) compares reaction kinetics to flow residence time, determining conversion levels in reactors.
Q.55Easy
For the decomposition of N₂O₅ following first-order kinetics with k = 0.0074 s⁻¹, what fraction of reactant remains after 300 seconds?
In cascade impaction for studying particle-phase reaction kinetics in reactors, which aerodynamic diameter range represents particles most suitable for chemical reaction on catalyst surfaces?
Answer: B
Particles in 0.5-5 μm range offer optimal surface area for catalytic reactions while maintaining reasonable diffusivity and reactivity characteristics.
Q.57Medium
For an isothermal CSTR processing a second-order reaction with inlet concentration C_A0 = 1 M and space time τ = 10 seconds, if k = 0.1 L/(mol·s), the outlet concentration is approximately:
Answer: B
For CSTR with second-order kinetics: C_A = [-1 + √(1 + 4kτC_A0)]/(2kτ) = [-1 + √(1 + 4)] / 2 ≈ 0.33 M
Q.58Medium
In fermentation processes, the Monod equation describes microbial growth rate kinetics. Which substrate concentration results in 90% of maximum growth rate?
Answer: A
From Monod equation: μ = (μ_max × [S])/(K_s + [S]). For μ = 0.9μ_max: [S] ≈ 9K_s
Q.59Hard
Which reactor configuration minimizes backmixing while maintaining high mass transfer rates for liquid-liquid reactions between immiscible phases?
Answer: B
Microfluidic segmented flow reactors provide plug-flow characteristics with enhanced interfacial area and mass transfer through controlled droplet generation in immiscible phases.
Q.60Medium
In a plug flow reactor (PFR) processing a first-order irreversible reaction with rate constant k = 0.5 min⁻¹, what is the space-time (τ) required to achieve 80% conversion?
