Multiply the specific entropy by the mass. Have you got a value for S° in cal/g*K? "cal/K" implies a given mass of water - or was it just a typo? Entropy is an extensive property!

It was not a typo. It's written cal/K on the book, so I just copied it.

I didn't think about it, actually, and I used the same value for both of the calculations.

I searched online and found that 16.75 is cal/mol*K, so I have to multiply for 5.55 and 11.11.

I did it and it works: I get 101 cal and the book 99.5 cal, so I think it's ok

Thank you! I'm glad it was just a little mistake and not a big one

Now I'm getting in trouble with the Clausius-Clapeyron equation, so be ready for another topic