### 4F.17

Posted:

**Mon Feb 10, 2020 3:24 am**Calculate the standard entropy of vaporization of water at 85 degreesC, given that its standard entropy of vaporization at 100. degreesC is 109.0 J/K*mol and the molar heat capacities at constant pressure of liquid water and water vapor are 75.3 J/K*mol and 33.6 J/K*mol, respectively, in this range.

First, you find the entropy change associated with the rise in temperature, so the equation should be used. However, the textbook solutions doesn't include n (moles) in the equation and instead just multiplies C_{p,m} with ln(T_{2}/T_{1})[/tex]. Why didn't they include n because don't you have to take into account that since C_{p,m} is C_{p}/n?

First, you find the entropy change associated with the rise in temperature, so the equation should be used. However, the textbook solutions doesn't include n (moles) in the equation and instead just multiplies C_{p,m} with ln(T_{2}/T_{1})[/tex]. Why didn't they include n because don't you have to take into account that since C_{p,m} is C_{p}/n?