The standard Gibbs free energy change (ΔG°) for a reaction at equilibrium is:

The correct answer is A: Zero. At equilibrium, ΔG = 0, which means ΔG° = -RT ln(K), and when ΔG° = 0, K = 1 (equilibrium)

For a venturimeter operating with water flow, the pressure at the throat is found to be lower than upstream. This pressure drop is used to:

The correct answer is A: Measure flow rate. Venturimeter uses Bernoulli's equation principle. The pressure difference between throat and upstream is related to flow velocity and can be used to calculate the volumetric flow rate.

For a reverse osmosis process, the concentration polarization effect results in:

The correct answer is A: Higher salt concentration at membrane surface than in bulk solution. Due to higher solute rejection, solutes accumulate near membrane surface, increasing local osmotic pressure and reducing driving force.

For fully developed laminar flow in a circular pipe with constant wall heat flux, which Nusselt number (Nu) is approximately correct?

The correct answer is B: Nu ≈ 4.36. For constant heat flux boundary condition (H1 type) in circular pipes with fully developed laminar flow, Nu ≈ 4.36. For constant wall temperature (H2), Nu ≈ 3.66.

For a binary gas mixture, the Stefan flow correction factor accounts for:

The correct answer is A: Net molar flow due to unequal molar diffusion rates. When one component condenses/reacts, equal molar counter-diffusion assumption breaks down. Stefan factor (B_m) corrects for net molar flow.

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Chemical Engineering

Process design, thermodynamics, reactions

247 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 11–20 of 247

Topics in Chemical Engineering

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

Q.11 Medium Thermodynamics

The reduced temperature T_r and reduced pressure P_r are defined using critical point parameters. A substance at T_r = 0.9 and P_r = 2.0 is classified as:

A Supercritical fluid

B Subcritical but compressed liquid

C Gas phase

D At critical point

Correct Answer: B. Subcritical but compressed liquid

EXPLANATION

T_r < 1 means T < T_c (subcritical). P_r = 2 means P > 2P_c (high pressure). This combination indicates compressed liquid state.

Test

Q.12 Medium Thermodynamics

The Gibbs phase rule F = C - P + 2 indicates that for a binary system with 2 phases:

A 1 degree of freedom exists (intensive variables)

B 2 degrees of freedom exist

C 3 degrees of freedom exist

D 0 degrees of freedom (invariant system)

Correct Answer: A. 1 degree of freedom exists (intensive variables)

EXPLANATION

F = C - P + 2 = 2 - 2 + 2 = 2, but if we consider only intensive variables at fixed P, then F = 1. Temperature alone determines composition of both phases.

Test

Q.13 Medium Thermodynamics

A heat engine operating between 800 K and 300 K has actual efficiency of 40%. Its carnot efficiency is:

A 62.5%

B 50%

C 40%

D 37.5%

Correct Answer: A. 62.5%

EXPLANATION

Carnot efficiency = 1 - T_c/T_h = 1 - 300/800 = 500/800 = 0.625 or 62.5%. Actual efficiency (40%) is always less than Carnot efficiency.

Test

Q.14 Medium Thermodynamics

The second law of thermodynamics can be expressed as:

A For isolated systems, ΔS_universe = 0 always

B For isolated systems, ΔS_universe ≥ 0, with equality for reversible processes

C Entropy always increases for spontaneous processes

D All spontaneous processes have negative ΔG

Correct Answer: B. For isolated systems, ΔS_universe ≥ 0, with equality for reversible processes

EXPLANATION

Second law states ΔS_univ ≥ 0 for isolated systems. Equality holds for reversible processes, inequality for irreversible processes (ΔS_univ > 0).

Test

Q.15 Medium Thermodynamics

The compressibility factor Z for a real gas at high pressure and low temperature typically shows:

A Z > 1, indicating repulsive forces dominate

B Z < 1, indicating attractive forces dominate

C Z = 1 at all conditions for real gases

D Z varies linearly with pressure

Correct Answer: B. Z < 1, indicating attractive forces dominate

EXPLANATION

At high P and low T, attractive intermolecular forces dominate over repulsion, making Z < 1. This indicates volume is less than ideal gas volume (PV < nRT).

Test

Q.16 Medium Thermodynamics

For an isothermal reversible expansion of 2 moles of ideal gas from 10 L to 50 L at 300 K:

A W = 2RT ln(5) ≈ 25.76 kJ

B W = nRT ln(V_f/V_i) ≈ 12.88 kJ

C W = -nRT ln(V_f/V_i) ≈ -12.88 kJ

D W = P(V_f - V_i) ≈ 80 kJ

Correct Answer: C. W = -nRT ln(V_f/V_i) ≈ -12.88 kJ

EXPLANATION

W = -∫PdV = -nRT ln(V_f/V_i) = -2×8.314×300×ln(5) ≈ -12.88 kJ. Work done by system is negative (work done on surroundings).

Test

Q.17 Medium Thermodynamics

The Legendre transformation from U(S,V) to F(T,V) replaces which variable pair?

A S with T, keeping V unchanged

B V with P, keeping S unchanged

C Both S and V with T and P

D T with S, keeping P unchanged

Correct Answer: A. S with T, keeping V unchanged

EXPLANATION

Helmholtz free energy F = U - TS is the Legendre transform of U with respect to entropy S, replacing it with conjugate variable T, while V remains unchanged.

Test

Q.18 Medium Thermodynamics

For a system at constant T and P, which statement about activity coefficient γ is true?

A γ = 1 always for ideal solutions

B γ > 1 indicates negative deviation from Raoult's law

C γ is independent of composition

D γ → 1 as mole fraction → 0 at infinite dilution

Correct Answer: A. γ = 1 always for ideal solutions

EXPLANATION

By definition, γ = 1 for ideal solutions. Activity coefficient accounts for non-ideal behavior. γ > 1 indicates positive deviation (activity > mole fraction).

Test

Q.19 Medium Thermodynamics

The fugacity coefficient φ for a pure component relates to which thermodynamic property?

A Deviation from ideal gas behavior at given T and P

B Ratio of entropy to enthalpy

C Only dependent on temperature

D Independent of pressure for all substances

Correct Answer: A. Deviation from ideal gas behavior at given T and P

EXPLANATION

Fugacity coefficient φ = f/P measures deviation from ideality. For ideal gas, φ = 1. It depends on both T and P and accounts for non-ideal intermolecular forces.

Test

Q.20 Medium Thermodynamics

In a throttling process (Joule-Thomson expansion), for an ideal gas, the enthalpy change is:

A Positive and equals PΔV

B Negative and equals -TΔS

C Zero

D Equal to internal energy change

Correct Answer: C. Zero

EXPLANATION

For an ideal gas, h depends only on temperature. Since throttling is isenthalpic (h constant), temperature remains constant, making ΔH = 0.

Test

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