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Daniel Fernandez 3H
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Postby Daniel Fernandez 3H » Fri Feb 03, 2017 1:59 pm

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?

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Re: 9.43

Postby kara_kremer_2N » Fri Feb 03, 2017 3:28 pm

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


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Re: 9.43

Postby Lillian_Lai_1K » Fri Feb 03, 2017 5:26 pm

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!!

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