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

The correct answer is B: Fluidization. Fluidization: particles suspended in gas/liquid flow with properties intermediate between fixed bed and fluid

For turbulent flow in smooth pipes, which equation is commonly used to estimate friction factor?

The correct answer is C: Blasius equation: f = 0.316/Re⁰·²⁵. Blasius equation is specifically for smooth pipes with 4000 < Re < 100,000. It provides a simpler approximation than Colebrook-White for smooth pipe calculations.

In a countercurrent absorption column, if the gas-phase mass transfer coefficient is k_G = 0.05 kmol/(m²·s·atm), the interfacial area 'a' = 200 m²/m³, and column cross-section = 5 m², the volumetric overall mass transfer coefficient is:

The correct answer is B: 50 kmol/(s·atm). Overall volumetric mass transfer = k_G × a × Volume = 0.05 × 200 × (5 × height). For unit height, K_G·a·V = 0.05 × 200 × 5 = 50 kmol/(s·atm).

A gas mixture contains N₂ (40% mole) and O₂ (60% mole) at 1 atm and 298 K. Calculate the partial pressure of O₂ in the mixture.

The correct answer is A: 0.6 atm. Partial pressure = Total pressure × Mole fraction. P_O₂ = 1 atm × 0.60 = 0.6 atm (Dalton's Law)

In the analysis of thermal stability of a convective system, the Richardson number (Ri) is used to compare natural and forced convection. Ri = Gr/Re². When Ri >> 1, what flow regime dominates?

The correct answer is B: Natural convection dominates. The Richardson number Ri = Gr/Re² compares buoyancy effects (Grashof) to external flow effects (Reynolds). When Ri >> 1, the Grashof number is much larger, meaning buoyancy forces dominate and natural convection is the primary mechanism.

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Chemical Engineering
Thermodynamics

Process design, thermodynamics, reactions

18 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 18

Topics in Chemical Engineering

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

Q.1 Hard Thermodynamics

In a desalination plant using reverse osmosis, work must be applied because:

A ΔG > 0 for the desalination process

B The process is adiabatic

C Heat must be removed from the system

D Entropy of the system decreases

Correct Answer: A. ΔG > 0 for the desalination process

EXPLANATION

Desalination (salt separation) is non-spontaneous: ΔG > 0. External work must be supplied to drive the process. This applies to RO and most separation processes.

Test

Q.2 Hard Thermodynamics

For a binary ideal solution at constant T and P, if we mix 1 mole of component A and 1 mole of component B, the entropy of mixing is:

A ΔS_mix = -R(ln 0.5 + ln 0.5) = R ln 4 > 0

B ΔS_mix = 0 (ideal solution)

C ΔS_mix = -R(x_A ln x_A + x_B ln x_B) < 0

D ΔS_mix depends on temperature

Correct Answer: A. ΔS_mix = -R(ln 0.5 + ln 0.5) = R ln 4 > 0

EXPLANATION

ΔS_mix = -nR Σx_i ln x_i. For equal moles: ΔS_mix = -2R(0.5 ln 0.5 + 0.5 ln 0.5) = R ln 4 > 0, always positive.

Test

Q.3 Hard Thermodynamics

An engineer needs to liquefy natural gas (primarily methane). The gas must be cooled below the inversion temperature because:

A Below inversion temperature, Joule-Thomson coefficient is positive

B Below inversion temperature, entropy increases

C Gibbs energy becomes negative only below inversion temperature

D Molecular interactions become repulsive below inversion temperature

Correct Answer: A. Below inversion temperature, Joule-Thomson coefficient is positive

EXPLANATION

Above inversion temperature (for methane ≈ 625 K), μ_JT < 0 (heating on expansion). Below it, μ_JT > 0 (cooling on expansion), enabling liquefaction.

Test

Q.4 Hard Thermodynamics

For a polytropic process PV^n = constant, if n = γ (heat capacity ratio), the process is:

A Isothermal

B Adiabatic

C Isobaric

D Isochoric

Correct Answer: B. Adiabatic

EXPLANATION

For adiabatic process of ideal gas, PV^γ = constant where γ = Cp/Cv. This is the defining equation for adiabatic polytropic process.

Test

Q.5 Hard Thermodynamics

For a reversible process at constant T and P, the minimum work required (excluding PV work) is:

A w_net = ΔG

B w_useful = -ΔG

C w_total = ΔH

D w_useful = ΔH - TΔS

Correct Answer: B. w_useful = -ΔG

EXPLANATION

Useful work (non-PV) available = -ΔG at constant T,P. This represents maximum useful work for spontaneous process or minimum work needed for non-spontaneous process.

Test

Q.6 Hard Thermodynamics

For a spontaneous process in an isolated system, the entropy production σ satisfies:

A σ = 0 always

B σ > 0 for irreversible processes, σ = 0 for reversible

C σ < 0 for all spontaneous processes

D σ is independent of process type

Correct Answer: B. σ > 0 for irreversible processes, σ = 0 for reversible

EXPLANATION

Entropy production σ = ΔS_total ≥ 0 for isolated systems. σ > 0 for irreversible spontaneous processes; σ = 0 for reversible processes (equilibrium).

Test

Q.7 Hard Thermodynamics

The chemical potential μᵢ of a component in a mixture relates to partial molar properties by:

A μᵢ = Ḡᵢ (partial molar Gibbs energy)

B μᵢ = Ūᵢ + Pv̄ᵢ - Ts̄ᵢ

C μᵢ = (∂G/∂nᵢ)_{T,P,n_j}

D All of the above

Correct Answer: D. All of the above

EXPLANATION

All statements define chemical potential from different perspectives. μᵢ is the partial molar Gibbs energy and equals (∂G/∂nᵢ)_{T,P,n_j}.

Test

Q.8 Hard Thermodynamics

In a steam power plant, the Rankine cycle efficiency increases when:

A Boiler pressure is increased

B Condenser temperature is decreased

C Both pressure and temperature variations are optimized

D Pump work is maximized

Correct Answer: C. Both pressure and temperature variations are optimized

EXPLANATION

Rankine cycle efficiency η = 1 - T_c/T_h improves with higher boiler temperature/pressure and lower condenser temperature, following Carnot efficiency limits.

Test

Q.9 Hard Thermodynamics

In a Joule-Thomson expansion of real gas at 298 K, a positive μ_JT (inversion coefficient) means:

A Temperature increases during throttling

B Temperature decreases during throttling

C No temperature change occurs

D Process is reversible

Correct Answer: B. Temperature decreases during throttling

EXPLANATION

μ_JT = (∂T/∂P)_H > 0 means temperature decreases with pressure drop during isenthalpic expansion. For most gases at room temp (except H₂ and He), μ_JT > 0, enabling gas cooling for liquefaction.

Test

Q.10 Hard Thermodynamics

For a real gas obeying virial equation PV/nRT = 1 + B/V̄, the internal energy change with volume at constant T is:

A Zero (same as ideal gas)

B Non-zero due to intermolecular forces represented by B(T)

C (∂U/∂V)_T = T(∂B/∂T)_P/V̄²

D Both B and C

Correct Answer: D. Both B and C

EXPLANATION

For real gases, (∂U/∂V)_T ≠ 0. From thermodynamic relations: (∂U/∂V)_T = T(∂P/∂T)_V - P. Using virial equation gives (∂U/∂V)_T = T(dB/dT)/V̄². Non-ideal behavior affects internal energy.

Test

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