All Free Chemical Engineering MCQs with Answers
Every Chemical Engineering question in the bank, across all chapters, each with the correct answer and a written explanation. Free and unlimited, with no account needed.
6,983 questions · page 182 of 350
- A. k/2
- B. ln k/2
- C. ln 2/k
- D. ln 0.5/k
Explanation: For a first-order irreversible reaction, CA/CA0 = e^-kt. At half-life CA/CA0 = 1/2, so kt = ln 2 and t1/2 = ln 2/k.
Correct answer: ln 2/k- A. Be more in CSTR than in PFR
- B. Depend on the temperature
- C. Be same in both cases
- D. Be more in PFR than in CSTR
Explanation: For a first-order reaction, a PFR gives the highest conversion for a specified volume and flow rate because every fluid element…
Correct answer: Be more in PFR than in CSTR- A. None of the above
- B. A step function
- C. A ramp function
- D. A Dirac delta function
Explanation: An ideal CSTR has an exponential exit age distribution, E(t) = (1/τ)e^(-t/τ), for t ≥ 0.
Correct answer: None of the above- A. May be lateral mixing of fluid
- B. Both A. and B.
- C. Should not be any mixing along the flow path
- D. Neither A. nor B.
Explanation: The ideal PFR permits complete lateral or radial mixing but has no axial mixing between fluid elements moving along the reactor.
Correct answer: Both A. and B.- A. 0
- B. 1
- C. 2
- D. 3
Explanation: Doubling concentration changes the rate by 2^n. Since the rate becomes four times larger, 2^n = 4 = 2^2, giving a second-order dependence…
Correct answer: 2- A. Temperature and pressure only
- B. Temperature and composition only
- C. Pressure and composition only
- D. All temperature, pressure and composition
Explanation: A homogeneous reaction rate can depend on composition through concentrations or activities, on temperature through the rate constant, and…
Correct answer: All temperature, pressure and composition- A. Is always greater for plug-flow reactor than for the single CSTR of the same volume
- B. Both A. and C. hold good
- C. Decreases with increasing conversion
- D. Statement in A. is wrong
Explanation: For a consecutive reaction in which an intermediate is the desired product, its relative yield generally falls as conversion increases…
Correct answer: Both A. and C. hold good- A. One of the reactants acts as a catalyst
- B. Catalysts have very high selectivity
- C. One of the products acts as a catalyst
- D. No catalyst is used
Explanation: In an autocatalytic reaction, a product formed by the reaction accelerates the same reaction, creating self-catalysis.
Correct answer: One of the products acts as a catalyst- A. 0
- B. > 150
- C. < 2100
- D. ∞
Explanation: Perfect mixing corresponds to maximum axial dispersion, so the dispersion number approaches infinity.
Correct answer: ∞- A. ∞
- B. > 1
- C. 1
- D. ≥ 1
Explanation: A finite number of mixed reactors in series only approximates plug flow.
Correct answer: ∞- A. Is same as heat of reaction at constant pressure
- B. Is the minimum energy which the molecules must have before the reaction can take place
- C. Varies as fifth power of the temperature
- D. Both B. and C.
Explanation: Activation energy is the energy barrier that reacting molecules must overcome for reaction to occur.
Correct answer: Is the minimum energy which the molecules must have before the reaction can take place- A. Same in both the reactors
- B. Higher in CSTR
- C. Higher in P.F. reactor
- D. Data insufficient; can't be predicted
Explanation: For a normal positive-order reaction, the plug-flow reactor maintains a higher reactant concentration over much of its length than the…
Correct answer: Higher in P.F. reactor- A. Usually equal to the residence time
- B. The reciprocal of the space velocity
- C. A measure of its capacity
- D. Both A. and B.
Explanation: Space time is reactor volume divided by inlet volumetric flow rate, and it is the reciprocal of space velocity.
Correct answer: Both A. and B.- A. Exothermic
- B. Autocatalytic
- C. Endothermic
- D. Autothermal
Explanation: In an autocatalytic reaction, the product promotes the reaction and partly offsets the decrease in reactant concentration as conversion…
Correct answer: Autocatalytic- A. Always equal to the total stoichiometric number of reactants
- B. An experimentally determined quantity
- C. Never fractional
- D. None of these
Explanation: Reaction order comes from the experimentally determined rate law, not directly from the stoichiometric equation.
Correct answer: An experimentally determined quantity- A. Increased temperature reduces the activation energy
- B. Collision frequency increases
- C. Fraction of molecules having threshold energy increases
- D. Value of threshold energy decreases
Explanation: From the Arrhenius equation, increasing temperature raises the fraction of molecules whose energy exceeds the activation or threshold…
Correct answer: Fraction of molecules having threshold energy increases- A. The composition of reactants remains constant along a flow path
- B. The conversion of the reactant varies from point to point along a flow path
- C. There is no lateral mixing of fluid
- D. There may be diffusion along the flow path
Explanation: In a plug-flow reactor, fluid elements move progressively downstream, so reactant conversion increases from point to point along the flow…
Correct answer: The conversion of the reactant varies from point to point along a flow path- A. Slurry
- B. Plug flow
- C. Homogeneous catalytic
- D. None of these
Explanation: Hydrogenation of vegetable oils uses a finely divided solid catalyst suspended in the liquid oil, with hydrogen gas dispersed through the…
Correct answer: Slurry- A. Freundlich
- B. Langmuir
- C. Tempkin
- D. None of these
Explanation: The BET equation extends the Langmuir monolayer adsorption concept to multilayer adsorption, allowing catalyst surface area to be…
Correct answer: Langmuir- A. First
- B. Zero
- C. Second
- D. Third
Explanation: For a second-order reaction, the half-life is t₁/₂ = 1/(kC_A0), so it is inversely proportional to the initial concentration.
Correct answer: Second