## 9.43

$\Delta G^{\circ}= \Delta H^{\circ} - T \Delta S^{\circ}$

$\Delta G^{\circ}= -RT\ln K$

$\Delta G^{\circ}= \sum \Delta G_{f}^{\circ}(products) - \sum \Delta G_{f}^{\circ}(reactants)$

Daniel Fernandez 3H
Posts: 21
Joined: Sat Jul 09, 2016 3:00 am

### 9.43

Hello!
9.43 Suppose that 50.0 g of H 2 O(l) at 20.0 \$C is mixed with 65.0 g of H 2 O(l) at 50.0 C at constant atmospheric pressure in a thermally insulated vessel. Calculate "S and "S tot for the process
What equation for S am I supposed to use and how do I mathematically connect the different temperatures and mass?
Thanks!

kara_kremer_2N
Posts: 20
Joined: Fri Jul 15, 2016 3:00 am

### Re: 9.43

At constant pressure, use $\Delta S=$Cvln (T2/T1) and S tot= kBln W1W2

$\Delta$T=Tfinal-Tinitial

Lillian_Lai_1K
Posts: 9
Joined: Wed Sep 21, 2016 2:57 pm

### Re: 9.43

You use the masses to find out how many moles of each substance you have:
The moles of the 20.0 deg C water is 50.0g/(18.015g/mol) = 2.78mol
The moles of the 50.0 deg C water is 65.0g/(18.015g/mol) = 3.61mol

Then you calculate the Final Temp:
[(2.78mol)(293.15K) + (3.61mol)(323.15K)] / (2.78mol + 3.61mol) = 310.1K

For each delta S, you use deltaS = nC[ln(Tfinal/Tinitial)]

For the delta S total, you add the change in entropy of the two H2O's

I hope this helped!!