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:
Answer: A
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
Q.162Medium
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.163Medium
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.164Medium
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.165Medium
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.
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Q.166Medium
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.167Medium
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.168Medium
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.169Medium
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.170Medium
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.171Medium
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.172Medium
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.173Medium
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.174Medium
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?
A CSTR operating at steady state processes an exothermic reaction. If the inlet temperature increases by 10°C while maintaining constant coolant flow rate, which parameter is most likely to increase?
Answer: B
Higher inlet temperature increases reaction rate (via Arrhenius equation) in an exothermic reaction, leading to higher conversion. Heat removal capacity depends on coolant flow and ΔT.
Q.176Medium
For a reversible reaction A ⇌ B with equilibrium constant Ke = 4, what is the maximum theoretical conversion in a batch reactor at equilibrium?
Answer: B
At equilibrium: Ke = [B]/[A] = 4. If initial [A]₀ = C, then at equilibrium: 4 = X/(1-X), solving X = 0.8 or 80%
Q.177Medium
In a semi-batch reactor where reactant A is fed continuously to a batch of reactant B, which advantage is realized?
Answer: A
Continuous feeding of A reduces the instantaneous reaction rate and heat generation, allowing better temperature control and potentially reducing side reactions.
Q.178Medium
A series of 3 identical CSTRs in cascade is used to process a first-order reaction with overall conversion X = 90%. Which statement is true?
Answer: C
For equal volume CSTRs in series processing first-order reaction: C = C₀/(1+kτ)ⁿ, showing exponential decrease in concentration.
Q.179Medium
In a fixed-bed catalytic reactor, what is the primary cause of catalyst deactivation by sintering?
Answer: B
Sintering involves migration of metal atoms on the catalyst surface, leading to agglomeration and reduction of active surface area, particularly at high temperatures.
Q.180Medium
Which reactor configuration would be best suited for a fast, highly exothermic reaction where precise temperature control is critical?
Answer: B
Semi-batch allows controlled feeding of reactants, limiting instantaneous heat generation while maintaining good mixing and temperature control.
