Entropy question

[toothgyal]

Advertisement - Members don't see this ad

hi everyone! please help me with this:
which has more entropy C4H10 or C3H8? ---> answer C4H10 has more entropy. ??? 😕

Wouldn't C3H8 have more entropy because its a smaller molecule and has more disorder than C4H10 which is more highly structured and complex having less disorder.. just my take on this question. help please. thanks in advance.

 

[JamesOSU]

hi everyone! please help me with this:
which has more entropy C4H10 or C3H8? ---> answer C4H10 has more entropy. ??? 😕

Wouldn't C3H8 have more entropy because its a smaller molecule and has more disorder than C4H10 which is more highly structured and complex having less disorder.. just my take on this question. help please. thanks in advance.

More bonds able to rotate, therefore higher entropy?

 

[klutzy1987]

The bigger something is trhe more entropy it will have.

 

[whateveryoulike]

hi everyone! please help me with this:
which has more entropy C4H10 or C3H8? ---> answer C4H10 has more entropy. ??? 😕

Wouldn't C3H8 have more entropy because its a smaller molecule and has more disorder than C4H10 which is more highly structured and complex having less disorder.. just my take on this question. help please. thanks in advance.

C3H8 = 12 sigma bonds that can freely rotate
C4H10 = 16 sigma bonds that can freely rotate

if you were to look at each bond as being able to rotate through 360 degrees, and that it could only be at an exact degree (not a reality, just stating this for the comparison) then C3H8 would have 12!*360! possible combinations while C4H10 would have 16!*360! possibe combinations. this lends to additional disorder.

PS - try to drop that mindset of more positioning for smaller molecules as it generally plays a much smaller factor compared to polarizability. aside from the bond angle issue already mentioned above, large molecules are more polarizable than smaller ones (lending to more entropy) which gives a trade off compared to your assumptions. the only time size would really matter (for your assumption) is in the gas phase, when the molecules are far enough apart that their relative size doesnt matter anyway. if size affected possible positioning in the gas phase, then it would needed to be taken into account in the ideal gas law, which it generally isnt. A good example for comparison is Iodine and Fluorine. Iodine is larger and more polarizable than Fluorine, giving it more possible immediate states. If you look in the appendix of one of your books youll see Fluorine has a lower entropy in every comparable state. this clearly doesnt follow your assumptions about size. Another example would be Potassium and Calcium. Potassium is more polarizable than Calcium and therefore has a larger entropy at all comparable states.

 

[toothgyal]

thanks guys.. 👍