Calculate the change in the entropies of the system and the surroundings, and the total change in entropy, when the volume of a sample of argon gas of mass 21 g at 298 K and 1.50 bar increases from 1.20 dm³ to 2.40 dm³ in (a) an isothermal reversible expansion, (b) an isothermal irreversible expansion against pex = 0, and (c) an adiabatic reversible expansion?
