The heat of vaporization of water is 40.66 kJ/mol at 373 K. The entropy of vaporization is approximately:
Answer: C
ΔS_vap = ΔH_vap/T = 40660 J/mol / 373 K ≈ 109 J/mol·K. This follows Trouton's rule (~85-105 J/mol·K for most liquids).
Q.405Medium
For a reversible process, the Clausius inequality states:
Answer: B
For reversible processes, ΔS = Q_rev/T. For irreversible processes, ΔS > Q_irrev/T. This is the Clausius inequality: dS ≥ dQ/T.
Advertisement
Q.406Medium
A cyclic heat engine operates between hot reservoir at 500 K and cold reservoir at 300 K. Maximum theoretical efficiency is:
Answer: B
Maximum efficiency is Carnot efficiency: η_max = 1 - T_cold/T_hot = 1 - 500300 = 0.40 = 40%. No heat engine can exceed this efficiency.
Q.407Medium
The heat capacity at constant pressure Cₚ is always greater than heat capacity at constant volume Cᵥ because:
Answer: B
Cₚ - Cᵥ = R (for ideal gas). At constant P, supplied heat does both internal energy and expansion work. At constant V, all heat goes to internal energy only.
Q.408Medium
For a real gas with van der Waals equation, the constants 'a' and 'b' represent:
Answer: B
In van der Waals equation (P + a/V²)(V - b) = RT, 'a' accounts for intermolecular attractive forces and 'b' represents excluded molecular volume. Both are positive constants.
Q.409Easy
Which process is represented by a horizontal line on a T-S (Temperature-Entropy) diagram?
Answer: C
On a T-S diagram, horizontal line means constant temperature (T = const), which is an isothermal process. A vertical line would represent isentropic process (S = const).
Q.410Medium
For a spontaneous process at constant T and P, which condition must be satisfied?
Answer: C
At constant T and P, spontaneity is determined by Gibbs free energy: ΔG < 0 for spontaneous process, ΔG = 0 for equilibrium, ΔG > 0 for non-spontaneous process.
Q.411Hard
The partial molar Gibbs energy at infinite dilution gives the chemical potential μ. For a component in ideal solution:
Answer: A
For ideal solutions, the chemical potential is μᵢ = μᵢ⁰ + RT ln(xᵢ), where xᵢ is the mole fraction. For non-ideal solutions, the activity aᵢ = γᵢxᵢ is used.
Q.412Hard
In a throttling process (Joule-Thomson expansion), for an ideal gas:
Answer: C
For ideal gas, enthalpy H depends only on temperature. In throttling (isenthalpic process), H = constant, so T = constant for ideal gas. For real gases, T may change based on Joule-Thomson coefficient.
Q.413Easy
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 entropy change for an isothermal irreversible expansion of an ideal gas from V₁ to V₂ is:
Answer: A
For an isothermal process of ideal gas, entropy depends only on volume ratio: ΔS = nR ln(V₂/V₁), regardless of reversibility
Q.415Easy
Which of the following represents a state function?
Answer: C
Internal energy (U), Enthalpy (H), Gibbs energy (G) are state functions. Work and heat are path functions
Q.416Easy
For a closed system at constant volume, the first law of thermodynamics simplifies to:
Answer: B
At constant volume, W = P×ΔV = 0. Therefore, ΔU = Q - 0 = Q
Q.417Easy
The standard Gibbs free energy change (ΔG°) for a reaction at equilibrium is:
Answer: A
At equilibrium, ΔG = 0, which means ΔG° = -RT ln(K), and when ΔG° = 0, K = 1 (equilibrium)
Q.418Medium
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?
