Chemical Engineering questions for GATE and PSU exams are built on a handful of core subjects applied in many ways. Practice spans fluid mechanics, heat transfer, mass transfer, chemical reaction engineering, thermodynamics, process control and instrumentation, and plant design economics. Numerical solutions carry the assumptions written out, because the assumption is usually what separates a correct answer from a plausible one.
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.202Medium
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.203Medium
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.204Medium
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?
For ideal gases, f = P (fugacity equals pressure), so φ = f/P = 1. Real gases have φ ≠ 1
Q.210Medium
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.211Medium
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.212Medium
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.213Medium
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.214Medium
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.215Medium
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.216Medium
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.217Medium
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.218Medium
The partial molar volume of a component in solution is:
Answer: B
Partial molar volume V̄ᵢ = (∂V/∂nᵢ)T,P represents the actual volume increase when 1 mole of i is added. It varies with composition and differs from pure component molar volume.
Q.219Medium
For a binary ideal solution at constant T and P, the Gibbs energy of mixing is:
Answer: D
For ideal solutions: ΔH_mix = 0 and ΔS_mix = -R(x₁ ln x₁ + x₂ ln x₂), so ΔG_mix = -TΔS_mix = RT(x₁ ln x₁ + x₂ ln x₂) < 0, making mixing spontaneous.
Q.220Medium
The virial equation of state truncated after second term is: PV = nRT(1 + B(T)P/RT). What does B(T) represent?
Answer: D
B(T) is the second virial coefficient that accounts for molecular interactions. It corrects ideal gas behavior and is temperature-dependent, directly representing non-ideality.
