Calculate the change in 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 dm^3 to 4.60 dm^3 in (i) an isothermal reversible expansion: (ii) an isothermal irreversible expansion against p _ex = 0: (iii) an adiabatic reversible expansion.