Help With Question 8.39  [ENDORSED]

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Simone Seliger 1C
Posts: 30
Joined: Fri Sep 25, 2015 3:00 am

Help With Question 8.39

Postby Simone Seliger 1C » Thu Jan 19, 2017 10:12 pm

What is the value 6.01 kJ.mol^-1 representing in this answer? It has the same units as Gibbs free energy, but when I looked in the index that value for H20 was way different. Shouldn't it be the heat constant for that molecule? And where can we find that value in the textbook?

Thanks!

Christopher Reed 1H
Posts: 33
Joined: Wed Sep 21, 2016 2:57 pm
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Re: Help With Question 8.39  [ENDORSED]

Postby Christopher Reed 1H » Thu Jan 19, 2017 10:35 pm

Hello!

The value of 6.01 kJ/mol is the enthalpy of fusion for water. I would not concern yourself with Gibbs Free Energy at the moment.

You need to use the enthalpy of fusion because your starting sample is ICE and you want your final to be a LIQUID. In other words, the enthalpy of fusion is for when you are considering the phase change (temperature does not change!) from solid water to liquid water.

You would use the heat capacity of LIQUID WATER to find how much energy it would take to raise the sample to 20 degrees Celsius.

In summary:

will give you the energy needed to change ice at 0 degrees Celsius to liquid at 0 degrees Celsius. The variable n here represents moles.
will tell you the energy needed to raise the temperature of liquid water by X degrees Celsius. The variable C represents the specific heat capacity of liquid water.

If you have any further questions please ask.

Simone Seliger 1C
Posts: 30
Joined: Fri Sep 25, 2015 3:00 am

Re: Help With Question 8.39

Postby Simone Seliger 1C » Fri Jan 20, 2017 5:02 pm

Ok, thanks so much.

I was confused because in my discussion my TA gave us a different value for enthalpy of fusion that we used in an example for water. It was 334 J/mol.


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