Irreversible and reversible expansion, 6th edition 8.11

[Arianna Ko 2E]

Do you know if a process is an irreversible expansion if you relatively come to the same original volume value? I'm confused as to how we know from information given whether or not a process is reversible or irreversible. I feel that (a) and (b) given are switched in the solutions manual, or am I just confused.

[KimGiang2F]

An irreversible process is one by which the expansion against an external pressure differs by a finite (measurable) amount from the pressure of the system. Whereas, a reversible process is one that can be reversed by infinitesimal contributions within a variable. Even though the final volumes are the same for both (a) and (b), the external pressure of (a) and (b) are different by which the external pressure for reversible reactions is matched to the pressure of the gas at every stage of reversible expansions (P=nRT/V). I think normally within problems, we'd be provided with the information of whether a process is irreversible or reversible.

[jonathanjchang2E]

We know that part a in 8.11 is referring to irreversible expansion because the gas is expanding against a constant pressure of 1 atm. In a reversible expansion, the external pressure is always equal to the pressure of the gas.