## 9.15

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

Chew 2H
Posts: 34
Joined: Fri Sep 29, 2017 7:05 am

### 9.15

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

Anika_Patel_1G
Posts: 32
Joined: Fri Sep 29, 2017 7:06 am

### Re: 9.15

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
Posts: 57
Joined: Fri Sep 29, 2017 7:07 am
Been upvoted: 1 time

### Re: 9.15

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
Posts: 53
Joined: Sat Jul 22, 2017 3:01 am

### Re: 9.15

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

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.