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