In a batch reactor operating at constant volume, the rate of reaction for a first-order reaction A→B is -rA = kCA. If the initial concentration is 2 mol/L and k = 0.1 min⁻¹, what will be the concentration after 10 minutes?
What is the primary advantage of a plug flow reactor (PFR) over a continuous stirred-tank reactor (CSTR) for reactions with high activation energy?
Answer: C
PFR provides higher conversion than CSTR for the same volume because of better concentration gradient utilization and no back-mixing of unreacted material
Q.23Easy
In the context of reaction kinetics, which statement best describes the rate-determining step (RDS) in a multi-step reaction mechanism?
Answer: B
The rate-determining step is the slowest elementary step in the reaction mechanism, which governs the overall rate of the reaction regardless of its position in the sequence
Q.24Medium
For a second-order reaction A+B→C with equal initial concentrations of 1 mol/L, if the rate constant is 0.5 L/(mol·min), what is the time required for 50% conversion?
Answer: A
For second-order reaction with CA0 = CB0: 1/CA - 1/CA0 = kt. At 50% conversion, CA = 0.5. So (01.5 - 11) = 0.5×t gives t = 2 minutes
Q.25Medium
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%
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Q.26Medium
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.27Medium
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.28Easy
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.29Medium
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
Q.30Medium
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.31Medium
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.32Hard
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.33Hard
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.35Medium
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.36Hard
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.37Hard
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.38Hard
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.39Medium
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.40Easy
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.
