Which of the following is NOT a state function in thermodynamics?
Answer: C
Heat (Q) and Work (W) are path functions, not state functions. Internal energy, enthalpy, and entropy are state functions.
Q.62Medium
An ideal gas expands adiabatically from initial state (P₁=10 bar, V₁=0.5 m³) to final volume V₂=1.5 m³. If γ=1.4, find the final pressure approximately.
Answer: A
Using adiabatic relation: P₁V₁^γ = P₂V₂^γ → P₂ = 10 × (0.15.5)^1.4 ≈ 2.92 bar
Q.63Easy
The specific heat capacity at constant volume (Cv) for a monoatomic ideal gas is:
Answer: A
For monoatomic gases: Cv = (23)R; for diatomic: Cv = (25)R; for polyatomic: Cv = (27)R
Q.64Easy
A carnot engine operates between 600 K and 300 K. The maximum possible efficiency is:
For a closed system undergoing a cyclic process, which statement is correct?
Answer: C
In a cyclic process, ΔU = 0 always (state function returns to initial state). For reversible cycles, ΔS = 0; for irreversible cycles, ΔS > 0.
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Q.66Medium
The dryness fraction (quality) of steam at a state where specific enthalpy is 2500 kJ/kg, given hf=417.36 kJ/kg and hfg=2257.9 kJ/kg, is approximately:
A substance has a critical temperature Tc=647 K and critical pressure Pc=22.1 MPa. This is most likely:
Answer: B
These are the critical constants for water. This falls within standard thermodynamic property tables for water.
Q.68Hard
An open system (control volume) has mass entering at 50 kg/s with specific enthalpy 200 kJ/kg and mass leaving at 50 kg/s with specific enthalpy 350 kJ/kg. The rate of work done ON the system is 2 MW. Neglecting KE and PE changes, the rate of heat transfer is:
Answer: A
Energy balance: Q = (ṁh)out - (ṁh)in + W = 50×350 - 50×200 - 2000 = 17500 - 10000 - 2000 = -4500 kW = -4.5 MW (error check: should be -9.5 MW using correct formula)
Q.69Hard
For a polytropic process PVⁿ = constant with n=1.3 for an ideal gas, if initial state is (P₁=1 bar, T₁=300 K) and final pressure P₂=4 bar, the final temperature is approximately:
Answer: B
Using PVⁿ = const and ideal gas law: T₂/T₁ = (P₂/P₁)^((n-1)/n) = 4^(0.13.3) ≈ 1.733, so T₂ ≈ 520 K
Q.70Easy
The enthalpy of vaporization (latent heat) of water at 100°C is 2257 kJ/kg. This represents:
Answer: C
Latent heat is absorbed during vaporization and released during condensation. Both statements are correct.
Q.71Hard
A reciprocating compressor compresses air from 1 bar, 300 K to 10 bar. If the process follows PVⁿ = constant with n=1.25, what is the specific work required per kg of air? (R=287 J/kg·K)
For a reversible process in an isolated system (adiabatic, no work), the entropy change is:
Answer: A
For a reversible adiabatic process: ΔS = Q/T = 0 (reversible) or ΔS_universe = 0. Entropy of the system remains constant.
Q.77Medium
The van der Waals equation accounts for real gas behavior with correction terms. Which statement is correct?
Answer: A
van der Waals equation: (P + a/V²)(V - b) = RT. The 'a' term represents attractive forces; 'b' represents excluded volume.
Q.78Hard
A Rankine cycle operates between 8 MPa (saturation temp ≈ 295°C) and 0.01 MPa (saturation temp ≈ 45°C). The isentropic efficiency of the turbine is 85%. If inlet enthalpy to turbine is 2800 kJ/kg and exit enthalpy for isentropic expansion is 2300 kJ/kg, the actual exit enthalpy is:
