Govt Exams
Otto cycle efficiency: η = 1 - 1/r^(γ-1) = 1 - 1/9^0.4 = 1 - 1/2.28 ≈ 0.558 or 55.8% ≈ 58%.
Maxwell relations come from the Schwarz theorem applied to thermodynamic potentials (U, H, F, G). For example, from dG = -SdT + VdP: (∂S/∂P)_T = -(∂V/∂T)_P.
For Brayton cycle: η = 1 - 1/r_p^((γ-1)/γ). As pressure ratio r_p increases, efficiency increases. This is why modern turbojets use high pressure ratios.
For a reversible process: ΔS_universe = ΔS_system + ΔS_surroundings = 0. The system's entropy can increase or decrease, but total entropy doesn't change.
Clausius-Clapeyron: dp/dT = L/(T·Δv), where L is latent heat of vaporization and relates pressure-temperature relationship at phase equilibrium.
For Carnot refrigerator: COP_ref = T_C/(T_H - T_C) = 250/(300-250) = 250/50 = 5.
The throttling process is isenthalpic (constant enthalpy). The enthalpy remains the same before and after the expansion valve.
For a monatomic ideal gas with 3 translational degrees of freedom: Cv = (3/2)R. For diatomic: (5/2)R; for polyatomic: (7/2)R.
For an irreversible process in an isolated system, total entropy increases (ΔS_total > 0). Heat transfer between bodies at different temperatures is irreversible.
First Law: ΔE_system = Q - W, where Q is heat added to system and W is work done by system. This is the IUPAC convention.