The same ideal gas is expanded from state $(P_{1}, V_{1}, T)$ to volume $V_{2}$ along two isothermal paths: I, reversible; II, a single step against a constant external pressure equal to the final pressure. Select the correct statement(s).

Answer: B, C, D

U

depends only on

T

, so

Δ U = 0

for both. The reversible path gives the maximum work, so

∣ w_{I} ∣ > ∣ w_{II} ∣

, and since

q = - w

here,

q_{I} > q_{II}

. Entropy is a state function, so

Δ S_{system}

is the same (

n R ln V_{2} / V_{1}

) for both paths; the statement claiming a larger

Δ S_{system}

for path I is false.