isothermal expansion

ipitydatfu

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?