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.82Hard
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.83Hard
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.84Hard
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.85Hard
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.
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Q.86Hard
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.87Hard
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.88Hard
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.89Hard
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.90Hard
For a second-order reaction in a PFR, increasing the inlet concentration while maintaining constant volumetric flow rate will result in:
Answer: C
In a PFR, conversion (fractional) depends on space-time and reaction kinetics but is independent of inlet concentration for a given residence time.
Q.91Hard
The Weisz-Prater criterion is used to determine:
Answer: A
Weisz-Prater number: CWP = (k''ρcRp²)/De. If CWP << 0.15, internal diffusion limitations are negligible.
Q.92Hard
For parallel reactions where A → B (desired) with rate constant k₁ and A → C (undesired) with rate constant k₂, the selectivity towards B is maximized by:
Answer: A
If Ea1 > Ea2, increasing temperature favors the desired reaction with higher activation energy, improving selectivity to B.
Q.93Hard
For a polymerization reaction in a batch reactor, the polydispersity index (PDI) and average molecular weight depend on:
Answer: B
PDI and molecular weight distribution in batch polymerization depend on the relative magnitudes of propagation and termination reactions and the degree of conversion achieved.
Q.94Hard
In consecutive reactions A → B → C (both first-order), maximum concentration of intermediate B occurs at which time?
Answer: B
Maximum [B] occurs when d[B]/dt = 0, giving t_max = ln(k₁/k₂)/(k₁-k₂) for k₁ ≠ k₂.
Q.95Hard
Thiele modulus (φ) represents the ratio of which two parameters in heterogeneous catalysis?
Answer: B
Thiele modulus φ = √(k·ρ_cat·a_s/D_eff) represents ratio of internal diffusion to surface reaction rate.
Q.96Hard
In a recycle reactor with recycle ratio R, what is the volume reduction factor compared to PFR for equivalent conversion?
Answer: A
Recycle reduces required volume by factor (1+R)/R compared to PFR for same conversion and residence time.
Q.97Hard
For homogeneous gas-phase reaction in batch reactor, if pressure increases at constant volume, what happens to reaction rate for 2A → Products?
Answer: C
Pressure increase increases concentration proportionally; for 2nd order rate = kC_A², quadrupling concentration increases rate 16-fold; doubling pressure quadruples rate.
Q.98Hard
The Maxwell relation that can be derived from Gibbs free energy is:
Answer: B
From dG = -SdT + VdP, the Maxwell relation is (∂S/∂P)ₜ = -(∂V/∂T)ₚ. This relates entropy-pressure change to volume-temperature change.
Q.99Hard
The partial molar Gibbs energy at infinite dilution gives the chemical potential μ. For a component in ideal solution:
Answer: A
For ideal solutions, the chemical potential is μᵢ = μᵢ⁰ + RT ln(xᵢ), where xᵢ is the mole fraction. For non-ideal solutions, the activity aᵢ = γᵢxᵢ is used.
Q.100Hard
In a throttling process (Joule-Thomson expansion), for an ideal gas:
Answer: C
For ideal gas, enthalpy H depends only on temperature. In throttling (isenthalpic process), H = constant, so T = constant for ideal gas. For real gases, T may change based on Joule-Thomson coefficient.
