## 4F.17

Volume: $\Delta S = nR\ln \frac{V_{2}}{V_{1}}$
Temperature: $\Delta S = nC\ln \frac{T_{2}}{T_{1}}$

JamieVu_2C
Posts: 108
Joined: Thu Jul 25, 2019 12:16 am

### 4F.17

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 $\Delta S = nC_{p,m}ln(T_{2}/T_{1})$ 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 $C_{p} = nC_{p,m}$ since C_{p,m} is C_{p}/n?

GFolk_1D
Posts: 101
Joined: Fri Aug 09, 2019 12:15 am

### Re: 4F.17

I believe you assume you are using one mole in the reaction