2015 DAT Destroyer, chem, #118

[nickh]

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Hey guys,

So in this question, it's saying C4H10 would have a higher entropy than C3H8, I just can't wrap my head around it because normally say hydrolysis, where things are getting broken down, that's when you see an increase in entropy. But comparing C4H10 to C3H8, it's a bigger molecule, then doesn't mean it should have a smaller entropy? As in it's more ordered?

Sorry, am I missing something here?😛

 

[nickh]

It's like when a liquid vaporizes, the delta S increases.

 

[DAT Destroyer]

Hey guys,

So in this question, it's saying C4H10 would have a higher entropy than C3H8, I just can't wrap my head around it because normally say hydrolysis, where things are getting broken down, that's when you see an increase in entropy. But comparing C4H10 to C3H8, it's a bigger molecule, then doesn't mean it should have a smaller entropy? As in it's more ordered?

Sorry, am I missing something here?😛

When comparing species in the same physical state, the larger the molecule the greater the molecular complexity and therefore the greater the amount of disorder. An easy way to rationalize this is that a larger specie has more electrons, atoms, energy levels, etc. As an exercise go to a general chemistry textbook and look up the value for the entropy of Pb versus Carbon then do it for C3H8 versus C4H10; larger species will almost always have greater disorder.

Hope this helps..