Govt. Exams
Entrance Exams
Third law of thermodynamics: The entropy of a perfect crystal at absolute zero is zero. S(0K) = 0 for perfect crystals.
In any cyclic process, system returns to initial state. Since U is a state function, ΔU = 0 for complete cycles.
Efficiency η = W/Q_h = 0.4. Work done W = 0.4 × 1000 = 400 J. Heat rejected Q_c = Q_h - W = 1000 - 400 = 600 J
At equilibrium, ΔG = 0. When ΔG < 0, reaction is spontaneous; when ΔG > 0, reaction is non-spontaneous.
Carnot efficiency = 1 - (T_cold/T_hot) = 1 - (300/400) = 1 - 0.75 = 0.25 = 25%
Internal energy depends only on initial and final states, not on the path. Heat and work are path functions.
By first law of thermodynamics: ΔU = q - w = 500 - 200 = 300 J (where w is work done by the system)
Efficiency η = W/Q_in = (Q_in - Q_out)/Q_in = (500 - 300)/500 = 200/500 = 0.40 = 40%
In an adiabatic process, Q = 0 (no heat transfer). From first law: ΔU = Q - W = 0 - W = -W, so ΔU = -W.
For an isothermal reversible process: W = nRT ln(V₂/V₁) = P₁V₁ ln(V₂/V₁). Since V₂ > V₁, work is positive (work done by the gas).
