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Chew 2H
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Joined: Fri Sep 29, 2017 7:05 am


Postby Chew 2H » Tue Feb 06, 2018 11:46 am

Could someone help with how to solve 9.15? I'm not sure where to start

Posts: 32
Joined: Fri Sep 29, 2017 7:06 am

Re: 9.15

Postby Anika_Patel_1G » Tue Feb 06, 2018 12:01 pm

The pressure at a phase change is constant so we can change the formula deltaS=q/T to deltaH/T. You then plug in the delta H fusion of water and divide it by the temperature given (298.15 K). You then need to multiply this number by the number of moles (1.00) to fix the units.

Sabrina Dunbar 1I
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Re: 9.15

Postby Sabrina Dunbar 1I » Tue Feb 06, 2018 12:04 pm

Using the equation ∆S=q/T, we can substitute ∆Hº for q, and the the appendix provides the value for that variable. Because the given ∆Hº is per mole, multiply the numerator by the number of moles in the sample to then produce the correct value. Hopefully this will give you a good jumping off point to start the problem!

Alyssa Parry Disc 1H
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Joined: Sat Jul 22, 2017 3:01 am

Re: 9.15

Postby Alyssa Parry Disc 1H » Wed Feb 07, 2018 8:52 pm

Why is the deltaH fusion negative though? I don't understand

Charles Ang 1E
Posts: 50
Joined: Thu Jul 13, 2017 3:00 am

Re: 9.15

Postby Charles Ang 1E » Fri Feb 09, 2018 10:29 pm

Delta H fus is negative because the phase change is going from a liquid to a solid. Since a solid has less possible positions for its atoms, there is less entropy. So the system is losing entropy when it freezes.

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