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 183 of 350
- A. V
- B. V/n
- C. V.n
- D. 1/V
Explanation: PFR volumes in series add, and a series of ideal plug-flow sections behaves like one ideal PFR having the same total volume.
Correct answer: V- A. Linearly with time
- B. Exponentially with time
- C. Very abruptly towards the end of the reaction
- D. Logarithmically with time
Explanation: Integrating the first-order rate law gives C_A = C_A0e⁻ᵏᵗ, so concentration falls exponentially rather than linearly with time.
Correct answer: Exponentially with time- A. 3
- B. 4
- C. 6
- D. 10
Explanation: For first-order decay, each half-life reduces the remaining amount by half.
Correct answer: 4- A. None of the above
- B. Reaction
- C. External mass transfer
- D. Diffusion within the pellet
Explanation: A much lower concentration at the pellet centre than at its surface indicates a steep internal concentration gradient.
Correct answer: Diffusion within the pellet- A. Ideal tubular-flow reactor
- B. Batch reactor
- C. Slurry reactor
- D. CSTR
Explanation: Space time is based on reactor volume and inlet volumetric flow, making it convenient for sizing an ideal tubular-flow reactor.
Correct answer: Ideal tubular-flow reactor- A. Ideal plug flow
- B. Dead zone
- C. Bypass
- D. Channelling
Explanation: A long tail means some material remains in the packed bed much longer than the main flow, which indicates stagnant or dead regions.
Correct answer: Dead zone- A. Inversely proportional to
- B. Independent of
- C. Proportional to
- D. Proportional to the square of
Explanation: Without a chain mechanism, doubling the amount of catalyst doubles the available active surface and hence the overall rate, provided…
Correct answer: Proportional to- A. Decreases
- B. Remains unchanged
- C. Increases
- D. Unpredictable from the data
Explanation: For an exothermic reversible reaction, increasing temperature shifts equilibrium toward the reactants, so the equilibrium conversion…
Correct answer: Decreases- A. CSTR of volume V
- B. PFR of volume V
- C. CSTR of volume V/X
- D. PFR of volume V/X
Explanation: Ideal PFRs in series behave as one continuous PFR because each element experiences the same plug-flow progression.
Correct answer: PFR of volume V- A. Equilibrium constant is infinite
- B. Fractional conversion of 'A' at equilibrium is unity
- C. All A., B. and C.
- D. Concentration of 'A' at equilibrium is zero
Explanation: An irreversible reaction is the limiting reversible case with an infinite equilibrium constant.
Correct answer: All A., B. and C.- A. 18
- B. 24
- C. 6
- D. 12
Explanation: A 75% conversion leaves 25% of A, or one-fourth of its initial amount. For a first-order reaction this requires two half-lives, so the…
Correct answer: 24- A. 0.5
- B. -0.5
- C. 1
- D. 1.5
Explanation: For 2A → R, the change in total gas moles is 1 − 2 = −1 for every 2 moles of A consumed.
Correct answer: -0.53653. Arrhenius equation represents graphically the variation between the ______________ and temperature?
- A. Rate constant
- B. Frequency factor
- C. Rate of reaction
- D. Activation energy
Explanation: The Arrhenius relation, k = A exp(−Ea/RT), describes how the rate constant changes with temperature.
Correct answer: Rate constant- A. CSTR
- B. CSTR in series
- C. Recycle reactor
- D. Plug flow reactor
Explanation: A recycle reactor returns product to the feed, which is especially useful when the product catalyses the reaction because it supplies…
Correct answer: Recycle reactor- A. Higher
- B. Much higher
- C. Lower
- D. Much lower
Explanation: Cold-shot cooling removes heat by injecting a colder feed directly into the reacting mixture.
Correct answer: Much lower- A. Temperature of the system
- B. Time of reaction
- C. Extent of reaction
- D. Initial concentration of the reactants
Explanation: The Arrhenius relation, k=A exp(-E/RT), shows that the rate constant is primarily dependent on temperature for a given reaction.
Correct answer: Temperature of the system- A. 500
- B. 0
- C. 750
- D. ∞
Explanation: The dispersion number compares axial mixing with convective transport. Ideal plug flow has no axial dispersion, so D/(uL) approaches zero.
Correct answer: 0- A. Itself has very high activity
- B. Acts as a catalyst support
- C. Improves the activity of a catalyst
- D. All A., B. and C.
Explanation: A promoter is an additive that improves a catalyst's activity, selectivity, or stability, although it may have little catalytic activity…
Correct answer: Improves the activity of a catalyst- A. 1/(time)n
- B. (Concentration)1 - n/(time)
- C. (Concentration)n - 1/(time)
- D. None of these
Explanation: For an nth-order rate law, rate=kC^n, the units of k must make the result concentration per time.
Correct answer: (Concentration)1 - n/(time)- A. Extent of non-ideal flow in the vessel
- B. Reaction mechanism
- C. Activation energies of a reaction
- D. None of these
Explanation: The exit age distribution, or residence-time distribution, shows how long fluid elements remain in the vessel.
Correct answer: Extent of non-ideal flow in the vessel