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?
Answer: B
For CSTR: τ = (CA0 - CA)/(kCA) = X/(k(1-X)). Solving: 5 = X/(0.2(1-X)) gives X = 0.667 or 66.7%
Q.322Medium
Which of the following reactor types is most suitable for producing fine chemicals where precise temperature control is critical?
Answer: A
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
Q.323Medium
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?
Answer: B
Using ln(k2/k1) = (Ea/R)×(1/T1 - 1/T2) = (880000.314)×(3001 - 3101) ≈ 0.693, so k2/k1 ≈ 2.0
Q.324Easy
What does the selectivity parameter in a competing reaction system measure?
Answer: B
Selectivity S = rate of desired product formation / rate of undesired product formation, used to optimize reactor conditions for maximum desired product yield
Q.325Medium
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?
Answer: B
For reversible reactions, K = kf/kr = 0.01.02 = 5.0. This represents the ratio of forward to reverse rate constants at equilibrium
Advertisement
Q.326Medium
Which catalyst property is most important for industrial applications requiring high selectivity in parallel reactions?
Answer: B
Pore size distribution determines which reactants/products can access active sites, while active site specificity ensures desired reaction pathway is favored in parallel reactions
Q.327Medium
For an exothermic reaction, operating a CSTR at higher conversion requires:
Answer: C
Exothermic reactions generate heat; to achieve higher conversion without temperature runaway, external cooling must be provided to maintain reactor temperature within safe operating limits
Q.328Hard
In desorption-limited catalytic reactions, which step determines the overall reaction rate?
Answer: C
When desorption is the rate-limiting step, products stick to the catalyst and their slow removal prevents further reaction cycles, controlling overall rate
Q.329Hard
What is the significance of the Thiele modulus (φ) in heterogeneous catalysis?
In a semi-batch reactor for an exothermic consecutive reaction A→B→C, why is controlled addition of A preferred over charging all reactant initially?
Answer: B
Controlled addition keeps A concentration low, favoring formation of desired intermediate B while preventing its conversion to C, maximizing B yield through kinetic control
Q.331Medium
In industrial polymerization reactions, what is the primary role of chain termination reactions?
Answer: B
Chain termination by combination or disproportionation determines when polymer chains stop growing, directly controlling final molecular weight and its distribution
Q.332Hard
Which approximation allows simplification of complex enzyme kinetics to Michaelis-Menten form?
Answer: C
Michaelis-Menten kinetics can be derived using either steady-state approximation (d[ES]/dt = 0) or pre-equilibrium assumption (ES forms quickly), depending on reaction conditions
Q.333Hard
For gas-phase reactions in a packed bed reactor, the Peclet number (Pe) indicates:
Answer: A
Peclet number Pe = (uL)/D compares convective transport with axial dispersion; high Pe (>100) indicates plug flow, low Pe indicates significant backmixing
Q.334Hard
In the context of green chemistry and reaction engineering, which reactor configuration minimizes waste generation for a fast, highly exothermic reaction?
Answer: B
Microreactors provide exceptional heat/mass transfer, enable precise temperature control of exothermic reactions, minimize side reactions and waste, aligning with green chemistry principles
Q.335Medium
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.336Easy
In a batch reactor operating at constant temperature, the reaction A → B follows second-order kinetics with rate constant k = 0.05 L/(mol·min). If initial concentration of A is 2 M, what is the time required to reduce the concentration to 0.5 M?
Answer: A
For second-order reaction: 1/[A]t - 1/[A]0 = kt. Therefore, 01.5 - 21 = 0.05×t gives 2 - 0.5 = 0.05t, so t = 30 minutes.
Q.337Medium
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.338Medium
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.339Medium
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.340Medium
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.
