The Second Law of Thermodynamics (Physics)

Recall cards on the second law of thermodynamics. Reversible and irreversible processes: the definition of each, why nearly all real processes are irreversible, the quasi-static and dissipation-free requirements for reversibility, free expansion and spontaneous heat flow as irreversible processes, and the microscopic origin of irreversibility. Heat engines: the working substance, hot and cold reservoirs, the zero internal-energy change over a cycle, net work W = Q_h - Q_c, and thermal efficiency e = W/Q_h = 1 - Q_c/Q_h. Refrigerators and heat pumps as reversed heat engines: Q_h = Q_c + W, the coefficients of performance K_R and K_P, and why a coefficient of performance can exceed 1. Statements of the second law: the Kelvin and Clausius statements, the impossibility of a perfect heat engine or perfect refrigerator, and the equivalence of the two statements. The Carnot cycle: its four reversible steps (two isothermal, two adiabatic), the Carnot engine, Q_c/Q_h = T_c/T_h, the efficiency e = 1 - T_c/T_h, Carnot's principle, the equal efficiency of all reversible engines, and the Carnot coefficients of performance. Entropy: delta-S = Q/T for a reversible isothermal step, the integral form, entropy as a state function, the zero net entropy change over a reversible cycle, the joule-per-kelvin unit, phase-change entropy, and the entropy statement that total entropy never decreases. Entropy on a microscopic scale: entropy as disorder, the statistical second law, delta-S = nR ln(V2/V1) for isothermal expansion, the third law, and the approach to perfect order at absolute zero.