CSTR Exam 2026/2027 | 200 Practice Questions, Correct Answers & Detailed Rationales

CSTR Exam 2026/2027 | 200 Practice
Questions, Correct Answers & Detailed
Rationales
CSTR EXAM 2026/2027 | 200 PRACTICE QUESTIONS, CORRECT ANSWERS &
DETAILED RATIONALES

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DOCUMENT OVERVIEW

• This comprehensive practice exam contains 200 carefully selected questions
designed to assess mastery of Continuous Stirred-Tank Reactor (CSTR) theory,
design, operation, and practical applications across all fundamental and advanced
topics.

• Study this material by attempting questions without reference materials first,
reviewing detailed rationales to understand conceptual gaps, and targeting weak
topic areas with focused revision before attempting full practice sets.

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QUESTION 1: What is the primary characteristic of a Continuous Stirred-Tank
Reactor (CSTR)?

A) Perfect mixing with non-uniform concentration throughout the reactor

B) Complete uniform mixing throughout the reactor with exit stream composition
equal to internal composition

C) Plug flow pattern with no mixing

D) Partially mixed with concentration gradients

E) Laminar flow pattern with minimal turbulence

CORRECT ANSWER: B) Complete uniform mixing throughout the reactor with
exit stream composition equal to internal composition

RATIONALE: A CSTR is characterized by perfect or ideal mixing, meaning the
contents are completely mixed at all times. This results in uniform concentration

,throughout the reactor, and the exit stream composition equals the concentration
inside the reactor. This is the defining feature that distinguishes a CSTR from plug
flow reactors or other types of reactors.

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QUESTION 2: The space time (τ) in a CSTR is defined as:

A) The time required to process one reactor volume of feed

B) The actual time a molecule spends in the reactor

C) The ratio of outlet concentration to inlet concentration

D) The volume divided by mass flow rate

E) Both A and D are correct

CORRECT ANSWER: E) Both A and D are correct

RATIONALE: Space time (τ) is defined as V/v₀, where V is the reactor volume and v₀
is the volumetric flow rate of feed. This represents the time required to process one
reactor volume of feed. It is also equivalent to volume divided by volumetric flow
rate, making both statements A and D correct definitions of the same parameter.

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QUESTION 3: For a first-order reaction in a CSTR at steady state, the
conversion equation is:

A) X = kτ/(1 + kτ)

B) X = 1 - e^(-kτ)

C) X = kτ

D) X = 1/(1 + kτ)

E) X = e^(-kτ)

CORRECT ANSWER: A) X = kτ/(1 + kτ)

,RATIONALE: For a first-order reaction in a CSTR at steady state, the material balance
yields the conversion equation X = kτ/(1 + kτ), where k is the rate constant and τ is
the space time. This is derived from the steady-state material balance for a first-
order irreversible reaction in a CSTR. Option B is the conversion for a plug flow
reactor, making this distinction important.

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QUESTION 4: The mean residence time in a CSTR is:

A) Always equal to the space time

B) Greater than the space time for non-ideal reactors

C) Less than the space time

D) Dependent on reaction order only

E) Independent of flow rate

CORRECT ANSWER: A) Always equal to the space time

RATIONALE: For a CSTR, the mean residence time equals the space time (τ = V/v₀)
under steady-state conditions. Every molecule entering the reactor has the same
average time in the reactor, which equals the space time. This equality is a
fundamental property of ideal CSTR operation.

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QUESTION 5: Which statement best describes the residence time distribution
(RTD) in an ideal CSTR?

A) All molecules have exactly the same residence time

B) Follows an exponential distribution with probability density E(t) = (1/τ)e^(-t/τ)

C) Follows a normal distribution

D) No molecules leave before τ time

E) All molecules leave at exactly τ time

, CORRECT ANSWER: B) Follows an exponential distribution with probability
density E(t) = (1/τ)e^(-t/τ)

RATIONALE: An ideal CSTR exhibits an exponential residence time distribution
described by E(t) = (1/τ)e^(-t/τ). This means some molecules leave quickly while
others remain longer, but the probability follows this exponential decay pattern.
This is fundamentally different from plug flow, where all molecules have identical
residence times.

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QUESTION 6: In a CSTR mass balance for a non-reacting component, which
term is zero?

A) Accumulation term

B) Input term

C) Output term

D) Generation/consumption term

E) Both A and D

CORRECT ANSWER: E) Both A and D

RATIONALE: At steady state, the accumulation term is zero (d(nᵢ)/dt = 0). For a non-
reacting component, the generation/consumption term is also zero (Rᵢ = 0). The
mass balance becomes: Input = Output, which is the steady-state balance for a non-
reacting species in a CSTR.

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QUESTION 7: For an exothermic reaction in a CSTR, which factor is most
critical for safe operation?

A) Feed concentration

B) Conversion

C) Heat removal capacity and reactor size