Qualitative ways to find Entropy

Boltzmann Equation for Entropy:

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Thomas Hui 2J
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Joined: Wed Sep 21, 2016 2:55 pm

Qualitative ways to find Entropy

Postby Thomas Hui 2J » Fri Feb 10, 2017 11:42 am

How do you look at a molecule and rank their increasing standard entropy?

Example: Midterm W 2013, Q 5 B:
Arrange the following substances in order of increasing standard entropy:
CHF3 (g), CF4 (g), CH3F (g), CH2F2 (g)

Jerry Wang 1L
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Joined: Fri Jul 22, 2016 3:00 am

Re: Qualitative ways to find Entropy

Postby Jerry Wang 1L » Fri Feb 10, 2017 12:18 pm

Firstly, you would rank by the complexity (i.e number of atoms) of the molecule. Those with higher complexities will have higher entropies. However, in this case, the molecules all have the same number of atoms. So, in order to arrange these molecules by entropies, we proceed to look at molar weight of these molecules. Those with higher molar weights will have higher entropies. The molecules below can be arranged according to their molar weights, which should give the answer.

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Re: Qualitative ways to find Entropy

Postby Vandan_Patel_3L » Fri Feb 10, 2017 12:54 pm

You can also look at them through their structure and the statistical entropy for each through their degeneracy. This can be done by imagining that the molecules are cooled to 0K and seeing how many ways they can be at 0K to find their degeneracy.

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Postby Eric_pierce_3E » Sun Feb 12, 2017 4:06 pm

This was very helpful! thank you!

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