[Dolphinsiu]

In the reversible isothermal expansion of an ideal gas at 300 K from 1 to 10 L, where the gas has an initial pressure of 20.27 bar, calculate delta S for the gas. 
Ans. 15.56 JK-1mol-1

That's what I have calculated

Delta S = R ln (V2/V1) = 8.314 ln 10 = 19.14 JK-1mol-1

Why not 19.14, but 15.56? I feel very strange! What's wrong with my calculation?

[enahs]

Your answer and method is correct, for a reversible isothermal expansion.

Perhaps it is not a reversible isothermal expansion, or the book is just wrong. Check the errata for the book.

[Dolphinsiu]

Thank you!