## Qualitative ways to find Entropy

Boltzmann Equation for Entropy: $S = k_{B} \ln W$

Thomas Hui 2J
Posts: 11
Joined: Wed Sep 21, 2016 2:55 pm

### Qualitative ways to find Entropy

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
Posts: 10
Joined: Fri Jul 22, 2016 3:00 am

### Re: Qualitative ways to find Entropy

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.

Vandan_Patel_3L
Posts: 14
Joined: Wed Sep 21, 2016 2:55 pm

### Re: Qualitative ways to find Entropy

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.

Eric_pierce_3E
Posts: 13
Joined: Wed Sep 21, 2016 2:55 pm
This was very helpful! thank you!

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