CHEMISTRY COMMUNITY

What is the best way to tell if a system is reversible or irreversible?

Generally the question will deliberately state whether a system is reversible or irreversible.

For reversible systems:
w= -nRTln(V2/V1)
ΔS= q(rev)/ T @ a constant temperature
ΔS (where T1 --> T2) = nCln(T2/T1)

For irreversible systems:
w=-PΔV
ΔS= nRln(V2/V1)

^^ Adding onto Faith’s answer:

For reversible, the question will also state that system is isothermal.

Also, Ssys is the same for irreversible and reversible work.
The only difference is Ssurr.

Is a reversible system always isothermal?

Also remember that irreversible processes have more entropy than reversible processes.