Question: What is the entropy change when 1 mole of an ideal gas expands isothermally and reversibly from volume V1 to V2?

Options:

1. R ln(V2/V1)
2. R (V2 - V1)
3. 0
4. R ln(V1/V2)

Correct Answer: R ln(V2/V1)

Solution:

The entropy change for an isothermal and reversible expansion is given by ΔS = R ln(V2/V1).