One mole of ideal gas undergoes reversible isothermal expansion at 300 K from 1.0 L to 3.0 L. (a) Find the entropy change of the gas. (b) Find the entropy change of the surroundings (heat reservoir). (c) What is the total entropy change, and what does it signify? Solution: (a) Isothermal: delta_S_gas = Q_rev/T = W/T = n R ln(V2/V1)/... directly: delta_S = n R ln(V2/V1) = (1)(8.31) ln 3 = 9.13 J/K. (b) The reservoir loses heat Q = W = nRT ln3 = 2740 J, so delta_S_surr = -2740/300 = -9.13 J/K. (c) Total = 0 - exactly as expected for a reversible process; no net entropy is generated.