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.82Medium
Which reactor configuration provides the highest conversion for an endothermic reaction at equilibrium?
Answer: D
Membrane reactors shift equilibrium by removing products, overcoming equilibrium limitations in endothermic reactions.
Q.83Easy
For the reaction A + B → C, the rate law is r = kC_A²C_B. What is the overall order of reaction?
Answer: C
Overall order = sum of individual orders = 2 + 1 = 3.
Q.84Medium
In a CSTR operating at steady state, if volumetric flow rate increases while keeping concentration constant, what happens to conversion?
Answer: B
Increased flow rate reduces residence time τ = V/F. For CSTR, X = kτ/(1+kτ), so increased τ means decreased conversion.
Q.85Medium
What does the Damköhler number (Da) represent in reactor design?
Answer: B
Da = reaction rate/flow rate, determining whether reaction or flow dominates; Da >> 1 means reaction-limited.
Advertisement
Q.86Easy
For a reversible reaction at equilibrium, which statement is true?
Answer: B
At equilibrium, the net rate is zero because forward and reverse reaction rates are equal.
Q.87Medium
In a reactor with catalyst deactivation following first-order decay, what is the effect on reactant conversion over time?
Answer: B
Catalyst activity decays as a = exp(-k_d·t), causing effective rate constant to decrease, reducing conversion over time.
Q.88Easy
Which of the following statements about adiabatic reactors is correct?
Answer: C
In adiabatic reactors, Q = 0, so ΔT depends on heat of reaction (ΔH_r) and heat capacity of reactants.
Q.89Medium
For competitive-consecutive reactions: A → B (k₁), A → C (k₂), B → D (k₃), selectivity of B over C is defined as S_B/C = ?
Answer: A
For parallel reactions, instantaneous selectivity S_B/C = k₁/k₂, independent of time at low conversions.
Q.90Easy
What is the space-time (τ) in a PFR if reactor volume is 100 L and volumetric feed rate is 10 L/min?
Answer: C
Space-time τ = V/v₀ = 10100 = 10 min.
Q.91Medium
In microbial fermentation kinetics, the Monod equation models specific growth rate. What happens when substrate concentration >> K_s?
Answer: A
When [S] >> K_s, μ ≈ μ_max, making growth zero-order in substrate (Monod equation simplification).
Q.92Medium
For isothermal batch reactor with r = -dC_A/dt = kC_A^n, what is the integrated rate law for n=2?
Answer: A
For second-order: ∫dC_A/C_A² = -k∫dt gives 1/C_A - 1/C_A0 = kt.
Q.93Hard
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.94Easy
In CSTR, if inlet concentration C_A0 = 2 M, outlet concentration C_A = 0.5 M, what is fractional conversion?
Answer: C
Conversion X = (C_A0 - C_A)/C_A0 = (2 - 0.5)/2 = 0.75 or 75%.
Q.95Medium
For a reaction with activation energy E_a = 50 kJ/mol, by what factor does rate constant increase if temperature increases from 300K to 310K? (R = 8.314 J/mol·K)
Answer: B
Using Arrhenius: ln(k₂/k₁) = (E_a/R)(T₂-T₁)/(T₁T₂) ≈ 1.96, so k₂/k₁ ≈ 2.0
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.98Medium
In a CSTR operating at steady state with a first-order irreversible reaction A → B, if the volumetric flow rate is doubled while keeping reactor volume constant, how does the conversion of reactant A change?
Answer: B
In a CSTR, conversion depends on residence time (τ = V/Q). When volumetric flow rate Q doubles while V remains constant, residence time τ decreases by half. Since conversion X_A = kτ/(1+kτ) for first-order reaction, decreased τ leads to decreased conversion. This is a fundamental principle in reactor design for 2024-25 competitive exams.
