i was given this test problem a couple of days ago, that ha2 parts: 1 mol of ideal a) isothermal reversible at a Ti, Pi = 3 atm, Pf= 1 atm b)irreversible isothermal expansion under constant pressure (1 atm) . find the heat/work/internal energy, delta(H), entropy for both. attempt: part a is easy, that was well covered over the lecture/internets/various physics book but for part b, i wasnt so sure for my answers i put something in the lines of: U = q + w, deltaU = 0 therefore q = -w H = 0 (not too sure) i guess since its under constant pressure q = -w, and w = -p (delta v) q = (1 atm)(Vf - Vi) (volumes were found from ideal gas law) and Entropy S = Ssys + Ssur S = q/t + Ssur how do i get the entropy surroundings? and how far off am i? edit: bump no love for this thread?