Question on Destroyer Gen Chem 2010 #76 - entropy

[fuqele]

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Hi,
I just have a quick question about #76 on Destroyer GC section. The answer to the question is that C4H10 has higher entropy than C3H8, and I'm sort of wondering why.

My reasoning is that higher entropy->greater disorder. Since you need to put more atoms together to form C4H10, C4H10 would be more "ordered," thus lower entropy.

Destroyer's explanation to this question is totally opposite from my reasoning. It says that C4H10 has more atoms, and therefore greater molecular complexity, so it has a higher entropy.

The explanation also kind of makes sense to me, but I don't see anything wrong with my reasoning... any help?

Thanks 🙂

 

[Hope30]

Let see if my reason make sense. C4H10 is a longer chain and therefore has higher melting point. The melting point would cause higher entropy. The more trash you throw into the trash can, the more disorder it is.

My destroyer book will be here in a few days. Have less than two weeks to finish it. Darn.

 

[Bis-GMA111]

i don't know if i'm approaching this correctly but...

S=q(rev)/t

where q(rev) is the heat required for a reversible process and T is the absolute temperature.

so when you have a molecule that is higher in atomic weight you need more heat (q) to break the bonds apart, so it will have a higher q, hence a higher entropy

 

[needzmoar]

Hi,
I just have a quick question about #76 on Destroyer GC section. The answer to the question is that C4H10 has higher entropy than C3H8, and I'm sort of wondering why.

My reasoning is that higher entropy->greater disorder. Since you need to put more atoms together to form C4H10, C4H10 would be more "ordered," thus lower entropy.

Destroyer's explanation to this question is totally opposite from my reasoning. It says that C4H10 has more atoms, and therefore greater molecular complexity, so it has a higher entropy.

The explanation also kind of makes sense to me, but I don't see anything wrong with my reasoning... any help?

Thanks 🙂

Well to keep it simple, the more atoms a molecule has, the more microstates are available to that molecule. A microstate is kinda like a "configuration". Entropy is a measure of said configuration (from a stat. mechanics point of view).

edit: Forgot to address your second point.

I'm not sure what you mean by "more ordered" when you add atoms. When you add atoms, there are typically more vibrational/rotational modes available to it.