Higher Entropy

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Imani Johnson 1H
Posts: 14
Joined: Sat Jul 23, 2016 3:00 am

Higher Entropy

Postby Imani Johnson 1H » Thu Feb 02, 2017 10:29 am

If two molecules have the same molecular geometry, what determines which molecule has a higher entropy?

Sydmon Nguyen-Tran 1N
Posts: 21
Joined: Wed Sep 21, 2016 2:59 pm

Re: Higher Entropy

Postby Sydmon Nguyen-Tran 1N » Thu Feb 02, 2017 11:31 am

This is from a post about a year ago:
"S(gas) >> S(liquid) > S(solid), always.
For the same state, to compare entropy, think of the equation S = klnW (where k is Boltzmann's constant).
W = (number of states)^(number of particles).

With the same amount of moles, monatomic gases have more entropy because there is a greater number of particles. (So in the equation S = klnW, W is much greater.)

Additionally, more complex molecules have more possible states, making W larger and S larger.

Another general trend is that molecules with larger molar mass have larger entropy (compare say F2 and H2 in the appendix).

Particles at larger pressure have lower entropy (more compact).
Particles at larger volume have higher entropy (less compact).
Also, particles at higher temperature have higher entropy (more kinetic energy)."

So the answer to your question would be the molecule with the larger molar mass has the larger entropy

Sophia Eliopulos 2I
Posts: 21
Joined: Wed Sep 21, 2016 2:56 pm

Re: Higher Entropy

Postby Sophia Eliopulos 2I » Fri Feb 03, 2017 3:24 pm

It is also very important to remember the third law of thermodynamics which states that the entropies of all perfect crystals approach zero as the absolute temperature approaches zero (0 Kelvin). So, keeping this in mind, we also should look at the temperature these molecules are at.

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