November 30, 2020, 05:57:19 PM
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Topic: Heat of fusion  (Read 273 times)

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Offline cactusdanslocean

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Heat of fusion
« on: November 06, 2020, 02:21:12 AM »
Hello,
It's my first time on this forum but I hope that someone can help me!

I just did a lab about the heat of fusion of naphtalene and one of the question is to draw a graph of logx vs. (1/T) in order to find the ΔH° of naphtalene.

The only values that we have is the time, temperature and molar fraction of naphtalene/diphenylamine.

What do I calculate with the results in order to do the graph?
How is the molar fraction of naphtalene/diphenylamine helping me?

Thank you!

Offline cactusdanslocean

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Re: Heat of fusion
« Reply #1 on: November 06, 2020, 03:20:25 AM »
For more precision, I don't understand how we can determine the y axis (log X) with the results that are given. I searched and the only things that I could find is that somehow, we can obtain the K value somehow in order to apply the ln on that value.

To resume, I don't understand how to obtain the K values of this experiment.

ln k1/k2=-(ΔH°/R)((1/T1)-(1/T2))


Offline Borek

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Re: Heat of fusion
« Reply #2 on: November 06, 2020, 03:51:34 AM »
Something doesn't sound right.

Describe the lab you did.
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Offline cactusdanslocean

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Re: Heat of fusion
« Reply #3 on: November 06, 2020, 04:58:12 AM »
1. We weighed 5g of naphtalene.
2.We put the naphtalene in the test tube and heat in boiling water.
3. When the naphtalene is fused, we cooled the tube and checked the temperature at every 30sec until the solid is formed.
4. We combine the naphtalene and the diphenylamine to make mole fraction of naphtalene of 0.9, 0.8, 0.7 and 0.6.
5. We repeat 2. and 3.

Since that we have online classes because of the virus, I couldn't do it myself. The teacher only sent us the results.
The only question in the report that I can't understand is the one about finding ΔH° by creating a graphic with the results that I have.

Sorry for the lengthy explanation, I am myself confused.

I will share the results!

Offline Borek

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Re: Heat of fusion
« Reply #4 on: November 06, 2020, 12:42:43 PM »
Why some fields are marked green?

I wonder if it is not about reversing the idea mentioned here: https://en.wikipedia.org/wiki/Enthalpy_of_fusion#Solubility_prediction, napthalene/diphenylamine mixture can be reasonably close to an ideal solution.
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Offline cactusdanslocean

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Re: Heat of fusion
« Reply #5 on: November 07, 2020, 12:48:42 AM »
Oh.... yes it is!!

Sorry, it was not my brightest moment!
Thank you so much!

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