The Joule-Thomson coefficient μ_JT is negative for most gases at room temperature. This means:

The correct answer is A: Temperature increases during expansion. μ_JT = (∂T/∂P)_H. Negative coefficient means T increases with pressure drop (cooling requires very low T or high P).

A system absorbs 500 J of heat and does 200 J of work. The change in internal energy is:

The correct answer is A: 300 J. Using ΔU = Q - W, where Q = +500 J (absorbed) and W = +200 J (work done by system). Therefore, ΔU = 500 - 200 = 300 J.

The Peclet number (Pe = Re·Pr) in convective heat transfer indicates that:

The correct answer is C: Both (a) and (b) are correct. Pe represents relative importance of convection to diffusion: Pe >> 1 indicates convection dominance, Pe

The Prandtl number (Pr = Cp·μ/k) represents the ratio of which two transport properties?

The correct answer is A: Momentum diffusivity to thermal diffusivity. Prandtl number = ν/α where ν = μ/ρ (momentum diffusivity) and α = k/(ρCp) (thermal diffusivity). Pr > 1 means momentum diffuses faster.

For turbulent flow in a pipe, the Colburn analogy for mass transfer is: j_D = (Sh)/(Re × Sc^(1/3)). Which correlation best estimates j_D for smooth pipes?

The correct answer is A: j_D = 0.023 Re^(-0.2). For smooth pipes in turbulent flow, j_D ≈ 0.023 Re^(-0.2), which is analogous to the Dittus-Boelert correlation for heat transfer with the Colburn j-factor approach.

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Chemical Engineering

Process design, thermodynamics, reactions

133 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 41–50 of 133

Topics in Chemical Engineering

All Mass Transfer 100 Heat Transfer 100 Fluid Mechanics 100 Chemical Reaction Engineering 100 Thermodynamics 97

Q.41 Easy Chemical Reaction Engineering

For the decomposition of N₂O₅ following first-order kinetics with k = 0.0074 s⁻¹, what fraction of reactant remains after 300 seconds?

A 0.18

B 0.32

C 0.52

D 0.68

Correct Answer: A. 0.18

EXPLANATION

[A]/[A]₀ = e^(-kt) = e^(-0.0074×300) = e^(-2.22) ≈ 0.18 or 18% remains

Test

Q.42 Easy Chemical Reaction Engineering

For a reversible reaction A ⇌ B with forward rate constant k_f = 0.3 s⁻¹ and reverse rate constant k_r = 0.1 s⁻¹, what is the equilibrium constant K_c?

A 0.33

B 3.0

C 0.67

D 1.5

Correct Answer: B. 3.0

EXPLANATION

At equilibrium, K_c = k_f/k_r = 0.3/0.1 = 3.0. This represents the ratio of forward to reverse rate constants at equilibrium.

Test

Q.43 Easy Chemical Reaction Engineering

In a batch reactor operating at constant temperature, the reaction A → B follows second-order kinetics with rate constant k = 0.05 L/(mol·min). If initial concentration of A is 2 M, what is the time required to reduce the concentration to 0.5 M?

A 30 minutes

B 45 minutes

C 60 minutes

D 90 minutes

Correct Answer: A. 30 minutes

EXPLANATION

For second-order reaction: 1/[A]t - 1/[A]0 = kt. Therefore, 1/0.5 - 1/2 = 0.05×t gives 2 - 0.5 = 0.05t, so t = 30 minutes.

Test

Q.44 Easy Chemical Reaction Engineering

What does the selectivity parameter in a competing reaction system measure?

A The fraction of reactant converted per unit time

B The ratio of desired product to undesired product formation rates

C The efficiency of reactor mixing

D The temperature dependence of reaction rate

Correct Answer: B. The ratio of desired product to undesired product formation rates

EXPLANATION

Selectivity S = rate of desired product formation / rate of undesired product formation, used to optimize reactor conditions for maximum desired product yield

Test

Q.45 Easy Chemical Reaction Engineering

In the context of reaction kinetics, which statement best describes the rate-determining step (RDS) in a multi-step reaction mechanism?

A It is always the first elementary step

B It is the slowest step that controls the overall reaction rate

C It requires the lowest activation energy

D It occurs only in irreversible reactions

Correct Answer: B. It is the slowest step that controls the overall reaction rate

EXPLANATION

The rate-determining step is the slowest elementary step in the reaction mechanism, which governs the overall rate of the reaction regardless of its position in the sequence

Test

Q.46 Easy Chemical Reaction Engineering

What is the primary advantage of a plug flow reactor (PFR) over a continuous stirred-tank reactor (CSTR) for reactions with high activation energy?

A Lower residence time requirement

B Better temperature control

C Higher conversion for the same reactor volume

D Easier scale-up to industrial levels

Correct Answer: C. Higher conversion for the same reactor volume

EXPLANATION

PFR provides higher conversion than CSTR for the same volume because of better concentration gradient utilization and no back-mixing of unreacted material

Test

Q.47 Easy Chemical Reaction Engineering

In a batch reactor operating at constant volume, the rate of reaction for a first-order reaction A→B is -rA = kCA. If the initial concentration is 2 mol/L and k = 0.1 min⁻¹, what will be the concentration after 10 minutes?

A 0.736 mol/L

B 1.472 mol/L

C 0.368 mol/L

D 2.0 mol/L

Correct Answer: A. 0.736 mol/L

EXPLANATION

For first-order reaction: CA = CA0 × e^(-kt) = 2 × e^(-0.1×10) = 2 × e^(-1) = 2 × 0.368 = 0.736 mol/L

Test

Q.48 Easy Chemical Reaction Engineering

In a fluidized bed reactor (FBR), particles exhibit properties of both solids and fluids. What is this phenomenon called?

A Pseudoplasticity

B Fluidization

C Thixotropy

D Turbulence

Correct Answer: B. Fluidization

EXPLANATION

Fluidization: particles suspended in gas/liquid flow with properties intermediate between fixed bed and fluid

Test

Q.49 Easy Chemical Reaction Engineering

In an isothermal CSTR, if feed concentration C_A0 = 10 mol/m³ and outlet concentration C_A = 2 mol/m³, conversion is:

A 0.2 or 20%

B 0.8 or 80%

C 0.5 or 50%

D Cannot be determined

Correct Answer: B. 0.8 or 80%

EXPLANATION

Conversion X = (C_A0 - C_A)/C_A0 = (10-2)/10 = 0.8 = 80%

Test

Q.50 Easy Chemical Reaction Engineering

What is the order of reaction if the rate law is: rate = k[A]^(1/2)[B]?

A Zero-order

B 1.5-order

C First-order

D Second-order

Correct Answer: B. 1.5-order

EXPLANATION

Order = sum of exponents = 1/2 + 1 = 1.5 (fractional order, common in enzyme kinetics)

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