Which approximation is used in steady-state kinetics for enzyme reactions?
Answer: D
Both steady-state (d[ES]/dt = 0) and pre-equilibrium approximations are used in Michaelis-Menten derivation
Q.5Hard
For consecutive reactions A→B→C, the concentration of intermediate B is maximum at time t_max. This time depends on:
Answer: A
t_max = ln(k₂/k₁)/(k₂-k₁), depends only on rate constants, independent of [A]₀
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Q.6Hard
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.7Hard
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.9Hard
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.10Hard
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.11Hard
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.12Hard
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.13Hard
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.14Hard
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.15Hard
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.16Hard
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.17Hard
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.18Hard
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.19Hard
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.20Hard
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.
