Comparing Molar Entropies of Different Compounds

[Lilyana Villa 3L]

If we're given two different compounds and asked to determine which one has a higher molar entropy, would the larger molecule have a higher molar entropy since it would be more complex? Also, do we take into consideration the state of the compound (ex. gas, liquid, solid) when trying to figure out which one has a higher molar entropy, and if we do, how do we do that? I hope these questions make sense! Thank you in advance!

[Pranav Kadiyala 1A]

Gases have higher entropy than liquids, which have higher entropy than solids. This is prioritized and the most important. If the substances are in the same state, however, their complexity does matter, like you said - # of atoms, #of bonds, even # of electrons, potentially. Anything that adds complexity would increase entropy.

[Aayushi Jani 3A]

Yes, so a larger molecule (heavier molecule) has higher entropy since the energy levels are closer together, meaning they are more accessible. Complex molecules also have higher entropy (as seen through W since they would be able to occupy more orientations/positions). Ranking from highest entropy to lowest: gases > liquids > solids because entropy decreases as rigidity increases.

[Tessa House 3A]

The size of the molecule does affect the entropy because larger molecules will have more degeneracy. Molecules with larger masses also have higher entropies. You are correct that the entropy of gases, liquids, and solids have different entropies because the entropy of a gas is significantly higher than that of a liquid, which is also higher than the entropy of a solid. I believe some other factors like whether the molecule has double or single bonds also play a role because double bonds are not free to rotate, unlike single bonds, meaning their entropy wouldn't be as high as single bonds.

[Ximeng Guo 2K]

Generally, delta S of gas > liquid > solid. The IMFs also affect delta S as well.

[Gian Boco 2G]

Yes, take into account the phase (gas>liquid>solid) and the size/complexity of the particle. The larger/more complex, the greater the standard molar entropy.

[Madison Muggeo 3H]

I would say that the phases of the compounds should be taken into account first, so solid<liquid<gas. Entropy also increases with more complex molecules, which is something else to look out for.

[darchen3G]

Assuming molecules are all of the same state (solid/liquid/gas,) you need to know the number of conformations of the molecule. For example, a linear molecule would have lower entropy than a bent one.

[Ivy Tan 1E]

Hi!
You're right about more complex molecules having higher molar entropy (molar entropy increases with molar mass). The state of the compound should also be taken into account: solids have the least amount of molar entropy, then liquids, then gases, which have the highest molar entropy. Hope this helps!

[Brian Nguyen 2I]

Yes, larger molecules have more complexity and thus have more entropy. Also, gases will have more entropy than liquids, and liquids will have more entropy than solids. Solids have the least entropy out of the phases.