[orgo814]

I'm having some trouble understanding why for an isothermal irreversible process ΔS(surroundings) is equal to 0. I always thought that for irreversible there is still one sided work going on to/from the surroundings. Also- I always thought that adiabatic expansions always had a ΔS = 0 but for a problem I tried with an adiabatic expansion against Pex= 1.0 atm.. There was a calculated entropy. Insight into both of these would be great

[iScience]

Also- I always thought that adiabatic expansions always had a ΔS = 0

just speculation:from the Sackur-Tetrode equation, if we keep Q (from the U term) constant, we still have volume and work(from the U term) dependance.

http://en.wikipedia.org/wiki/Sackur%E2%80%93Tetrode_equation

[MrTeo]

I'm having some trouble understanding why for an isothermal irreversible process ΔS(surroundings) is equal to 0.

It is not. Where did you find this?

[orgo814]

My textbook

[iScience]

maybe you're referring to ΔU for the case of an isothermal expansion, in that case U=0 because it's isothermal. but not the entropy change