## 4F.17

$\Delta S = \frac{q_{rev}}{T}$

Mallika Singh 1G
Posts: 99
Joined: Sat Aug 24, 2019 12:16 am

### 4F.17

Could someone please post their scratchwork for this problem? I keep getting 2J/K for the entropy change.

4F.17 Calculate the standard entropy of vaporization of water at
85 C, given that its standard entropy of vaporization at 100 C is
109.0 J/Kmol and the molar heat capacities at constant pressure of liquid water and water vapor are 75.3 J/Kmol and 33.6 J/Kmol.

Harry Zhang 1B
Posts: 101
Joined: Sat Sep 14, 2019 12:16 am

### Re: 4F.17

Since entropy is a state function, to calculate the entropy of vaporization of water, you can use the equation: entropy change of heating the water from 85 to 100+entropy change of vaporizing the water at 100(constant temp.)+entropy change of cooling the vapor from 100 to 85. 75.3*ln[(100+273)/(85+273)]+109+33.6*ln[(85+273)/(100+273)]=111J/kmol.