A hydraulic jump occurs in open channel flow when:
Answer: B
Hydraulic jump is an abrupt, turbulent transition from supercritical to subcritical flow. Energy is dissipated during this process, causing a sudden rise in water surface.
Q.142Medium
The Moody diagram is used to determine friction factor for pipe flow. It shows that friction factor increases with:
Answer: B
In the Moody diagram, friction factor decreases with increasing Re in laminar region. In turbulent region, f increases with relative roughness (ε/D) and slightly decreases with increasing Re for rough pipes.
Q.143Medium
For a horizontal pipe with diameter variation from D₁ to D₂, if pressure difference is ΔP and ignoring losses, the velocity ratio V₁/V₂ is:
Answer: B
By continuity: A₁V₁ = A₂V₂. Since A = πD²/4, we get V₁/V₂ = A₂/A₁ = (D₂/D₁)². Pressure difference from Bernoulli validates this for incompressible flow.
Q.144Medium
Which type of reactor provides the best conversion for a reversible exothermic reaction?
Answer: C
PFR with heat removal maintains optimal temperature profile and continuous removal of products, favoring forward reaction equilibrium
Q.145Medium
In a CSTR operating at steady state, if residence time is doubled and inlet concentration remains constant, how does conversion change for a first-order reaction?
Answer: B
For CSTR: X = kτ/(1+kτ). Increasing τ increases conversion for first-order reactions
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Q.146Medium
For parallel reactions A→B and A→C, the selectivity of B over C is defined as:
Answer: A
Selectivity = rate of desired product formation/rate of undesired product formation
Q.147Medium
In a catalytic reaction, which parameter does NOT affect the rate of reaction?
Answer: C
Catalyst doesn't change ΔG or equilibrium position; it only lowers Eₐ. ΔG determines feasibility, not rate
Q.148Medium
For the reaction 2A → B, if initial concentration of A is 2 mol/L and concentration after 5 minutes is 1 mol/L, calculate rate constant (assuming second-order):
Answer: A
For 2nd order: 1/[A] = 1/[A]₀ + kt; 11 = 21 + k(5); k = 0.1 L/(mol·min)
Q.149Medium
The Damköhler number (Da) in chemical reactor design represents:
Answer: B
Da = kτ = (reaction rate constant × residence time), dimensionless number indicating reaction extent
Q.150Medium
In enzyme catalysis, what does the Michaelis-Menten constant (K_m) represent?
Answer: A
K_m represents substrate concentration [S] at which reaction velocity = V_max/2
Q.151Medium
For an exothermic reaction in an adiabatic reactor, what happens to the reaction rate as conversion increases?
Answer: C
Adiabatic reactor: no heat removal; exothermic reaction raises temperature, increasing k and hence rate
Q.152Medium
For autocatalytic reactions, which reactor gives highest conversion at equilibrium?
Answer: D
Equilibrium conversion is thermodynamically determined and independent of reactor type
Q.153Medium
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.154Medium
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.155Medium
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.156Medium
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.157Medium
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.158Medium
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.159Medium
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.160Medium
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
