For a first-order consecutive reaction A → B → C where k₁ = 0.1 min⁻¹ and k₂ = 0.05 min⁻¹, the maximum concentration of intermediate B occurs at approximately:

The correct answer is C: t = 13.86 minutes. For consecutive reactions, [B]max occurs at t_max = ln(k₁/k₂)/(k₁-k₂) = ln(2)/0.05 = 13.86 minutes

For a second-order reaction A+B→C with equal initial concentrations of 1 mol/L, if the rate constant is 0.5 L/(mol·min), what is the time required for 50% conversion?

The correct answer is A: 2 minutes. For second-order reaction with CA0 = CB0: 1/CA - 1/CA0 = kt. At 50% conversion, CA = 0.5. So (1/0.5 - 1/1) = 0.5×t gives t = 2 minutes

The mean free path (λ) in gas kinetic theory at standard conditions is approximately 60 nm. This implies that at atmospheric pressure, heat conduction in gases is primarily through:

The correct answer is A: Molecular diffusion. Small mean free path (60 nm

In hollow fiber membrane contactors for gas absorption, the advantage over conventional columns is:

The correct answer is A: Higher interfacial area per unit volume and no flooding. Hollow fiber contactors provide 500-1500 m²/m³ interfacial area (vs 100-400 m²/m³ in packed columns), operate without flooding, and enable independent control of gas and liquid flows.

The Nusselt number (Nu) relationship for laminar flow in a circular pipe is given by Nu = 3.66. What does this value represent?

The correct answer is B: The thermally developed laminar flow condition with constant wall temperature. The value of 3.66 is the fully developed Nusselt number for laminar flow in circular pipes under constant wall temperature (T_s constant) boundary condition, representing the thermal development region.

Home

Home › Subjects › Chemical Engineering › Thermodynamics

Chemical Engineering
Thermodynamics

Process design, thermodynamics, reactions

49 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 31–40 of 49

Topics in Chemical Engineering

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

Q.31 Medium Thermodynamics

At the critical point of a substance, which of the following is true?

A Surface tension becomes zero

B Viscosity becomes infinite

C Density equals both liquid and gas density

D Compressibility factor Z = 1

Correct Answer: A. Surface tension becomes zero

EXPLANATION

At the critical point, surface tension between liquid and gas phases vanishes because the distinction between phases disappears. The critical compressibility factor Zc ≈ 0.27 (not 1).

Test

Q.32 Medium Thermodynamics

A gas mixture at 298 K contains H₂ and N₂. If the mixture obeys Amagat's law and the partial volumes are equal, what is the mole fraction of H₂?

A 0.5

B 0.67

C 0.33

D 0.75

Correct Answer: A. 0.5

EXPLANATION

Amagat's law: V_total = V_H₂ + V_N₂. If partial volumes are equal, each is 50%, so x_H₂ = 0.5

Test

Q.33 Medium Thermodynamics

A throttle valve is used in a refrigeration cycle. This is an example of a(n) _____ process.

A Isentropic

B Isothermal

C Adiabatic irreversible

D Isochoric

Correct Answer: C. Adiabatic irreversible

EXPLANATION

Throttling is an adiabatic (Q=0) but irreversible process with no work done, causing entropy increase

Test

Q.34 Medium Thermodynamics

For a spontaneous process occurring at constant temperature and pressure, which condition must be satisfied?

A ΔH > 0 and ΔS > 0

B ΔG = ΔH - TΔS < 0

C ΔU < 0

D ΔS_universe = 0

Correct Answer: B. ΔG = ΔH - TΔS < 0

EXPLANATION

For spontaneity at constant T and P: ΔG = ΔH - TΔS must be negative (ΔG < 0)

Test

Q.35 Medium Thermodynamics

The fugacity coefficient (φ) for an ideal gas is:

A Always 1

B Always less than 1

C Always greater than 1

D Depends on temperature only

Correct Answer: A. Always 1

EXPLANATION

For ideal gases, f = P (fugacity equals pressure), so φ = f/P = 1. Real gases have φ ≠ 1

Test

Q.36 Medium Thermodynamics

When 100 g of ice at 0°C melts to water at 0°C at 1 atm, the entropy change is approximately (ΔH_fus = 334 J/g):

A 122 J/K

B 1.22 J/K

C 0.122 J/K

D 12.2 J/K

Correct Answer: B. 1.22 J/K

EXPLANATION

ΔS = ΔH/T = (100×334)/273.15 ≈ 122.3 J/K = 1.223 kJ/K ≈ 1.22 J/K (in kJ/K)

Test

Q.37 Medium Thermodynamics

For an open system, the steady flow energy equation relates enthalpy rather than internal energy because:

A Enthalpy is independent of pressure

B It accounts for flow work (PV) at inlet and exit

C Enthalpy is always greater than internal energy

D Entropy remains constant

Correct Answer: B. It accounts for flow work (PV) at inlet and exit

EXPLANATION

H = U + PV. The PV term represents flow work needed to push fluid across system boundaries in steady flow

Test

Q.38 Medium Thermodynamics

For a van der Waals gas, the critical compressibility factor (Z_c) is approximately:

A 0.27

B 1.0

C 0.5

D 0.375

Correct Answer: D. 0.375

EXPLANATION

For van der Waals gas: Z_c = P_c V_c/(nRT_c) = 3/8 = 0.375 (theoretical value)

Test

Q.39 Medium Thermodynamics

The Helmholtz free energy (A = U - TS) is the maximum useful work available at:

A Constant temperature and volume

B Constant temperature and pressure

C Constant volume and entropy

D Constant pressure and entropy

Correct Answer: A. Constant temperature and volume

EXPLANATION

Helmholtz free energy is defined at constant T and V. ΔA_max = W_useful (non-PV work)

Test

Q.40 Medium Thermodynamics

A reversible adiabatic process for an ideal gas follows PVᵞ = constant. If γ = 1.4 and initial pressure is 1 atm with volume 1 L, what is the final pressure when volume becomes 0.5 L?

A 2.64 atm

B 1.4 atm

C 2.0 atm

D 0.5 atm

Correct Answer: A. 2.64 atm

EXPLANATION

P₁V₁ᵞ = P₂V₂ᵞ → P₂ = P₁(V₁/V₂)ᵞ = 1×(1/0.5)^1.4 = 2^1.4 ≈ 2.64 atm

Test

1 2 3 4 5

All Subjects & Topics

Govt. Exams

Entrance Exams

Teacher Exams

Subjects

Quick Links

Chemical Engineering Thermodynamics

Chemical Engineering
Thermodynamics