For ideal gases, f = P (fugacity equals pressure), so φ = f/P = 1. Real gases have φ ≠ 1
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Q.426Easy
A system undergoes a process where Q = 100 J and W = 60 J. The change in internal energy is:
Answer: B
ΔU = Q - W = 100 - 60 = 40 J (First Law of Thermodynamics)
Q.427Medium
For a spontaneous process occurring at constant temperature and pressure, which condition must be satisfied?
Answer: B
For spontaneity at constant T and P: ΔG = ΔH - TΔS must be negative (ΔG < 0)
Q.428Medium
A throttle valve is used in a refrigeration cycle. This is an example of a(n) _____ process.
Answer: C
Throttling is an adiabatic (Q=0) but irreversible process with no work done, causing entropy increase
Q.429Hard
The Maxwell relation derived from Gibbs free energy (G = H - TS) is:
Answer: B
From dG = -SdT + VdP, the Maxwell relation is: (∂V/∂T)_P = -(∂S/∂P)_T
Q.430Medium
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?
Answer: A
Amagat's law: V_total = V_H₂ + V_N₂. If partial volumes are equal, each is 50%, so x_H₂ = 0.5
Q.431Hard
For a non-ideal binary mixture, the activity coefficient (γᵢ) deviates from unity when:
Answer: B
Activity coefficients account for non-ideal behavior due to intermolecular forces and molecular size differences
Q.432Hard
The Clausius-Clapeyron equation relates vapor pressure to temperature. Which assumption is NOT required for its derivation?
Answer: D
Clausius-Clapeyron requires phase equilibrium, constant ΔH_vap, ideal gas approximation, but works for closed systems
Q.433Easy
A reversible adiabatic process is also known as:
Answer: A
A reversible adiabatic process has constant entropy (dS = 0), which defines an isentropic process. This is a fundamental concept in thermodynamics.
Q.434Easy
The enthalpy change for a constant pressure process equals:
Answer: A
At constant pressure, ΔH = qₚ (heat at constant pressure). This is the definition of enthalpy and its primary application.
Q.435Medium
At the critical point of a substance, which of the following is true?
Answer: A
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).
Q.436Medium
For an ideal gas undergoing isothermal expansion from V₁ to V₂, the entropy change is:
Answer: A
For isothermal process: dS = dq_rev/T = nR dV/V, integrating gives ΔS = nR ln(V₂/V₁). Temperature is constant, so entropy change depends only on volume change.
Q.437Medium
The residual property in thermodynamics is defined as the difference between:
Answer: A
Residual properties (M^R) account for non-ideal behavior: M^R = M_real - M_ideal at same T and P. Essential for calculating properties of real gases and mixtures.
Q.438Medium
A process where temperature and pressure both increase is most likely:
Answer: A
In polytropic compression with n between 1 and γ, both T and P increase as volume decreases. Isentropic expansion decreases T and P. Throttling and isothermal keep T constant.
Q.439Medium
The compressibility factor Z for a real gas at high pressures typically:
Answer: D
At low T, attractive forces dominate (Z < 1). At high T, repulsive forces dominate (Z > 1). The Boyle temperature is where Z ≈ 1. Pressure and temperature both influence Z significantly.
Q.440Easy
In a constant volume process, the heat added to the system equals:
Answer: A
For constant volume: W = 0, so Q = ΔU from first law (ΔU = Q - W). This is isochoric process where all heat goes to internal energy change.
