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Midterm 6A (Multiple Choice)

Posted: Tue Feb 27, 2018 12:52 am
by Nicole 1F
Question 6A Answer: C8H18(l) (at 298 K) has higher molar entropy than CH4(g), because C8H18 is a larger molecule than CH4, and larger molecules have more chemical bonds and can store energy in more ways than smaller molecules.

How do you know that C8H18 has a higher molar entropy when it is a liquid and CH4 is a gas? How much larger does the molecule have to be so that the phases don't determine the higher molar entropy?

Re: Midterm 6A (Multiple Choice)

Posted: Tue Feb 27, 2018 9:03 am
by Priyanka Bhakta 1L
In terms of entropy, the phase is always more deterministic of entropy than molecule size. Since CH4 is a gas, its phase already makes it have higher entropy than any sized liquid molecule.

Re: Midterm 6A (Multiple Choice)

Posted: Tue Feb 27, 2018 9:21 am
by Tiffany Dao 1A
Just in general, gases have the most freedom to move, then liquids and then solids have the least. There are bonds keeping the liquid together more, while for a gas they bounce off each other with more momentary interactions.

Re: Midterm 6A (Multiple Choice)

Posted: Tue Feb 27, 2018 11:02 am
by Jingyi Li 2C
That is the entropy for gases are much larger than liquids and solids. Compare to this, the size of molecules has less effect.

Re: Midterm 6A (Multiple Choice)

Posted: Tue Feb 27, 2018 11:18 am
by Harrison Wang 1H
When determining the molar entropy of molecules, the phase of the molecule takes priority over size. That is, only if both molecules are in the same phase does size matter. Otherwise, the entropy of gases >> liquids > solids