## entropy of heavy vs. light molecules

$\Delta S = \frac{q_{rev}}{T}$

Kayla Danesh 1F
Posts: 38
Joined: Thu Jul 13, 2017 3:00 am

### entropy of heavy vs. light molecules

In figure 9.13 in the textbook, the caption states the following: "The energy levels of a particle in a box are more widely spaced for (a) light molecules than for (b) heavy molecules. As a result, the number of thermally accessible levels, as shown
by the tinted band, is greater for heavy molecules than for light molecules at the same temperature, and the entropy of the substance with heavy molecules is correspondingly greater."

Can someone please explain why substances made of heavier molecules have a greater entropy? Thank you.

Ryan Sydney Beyer 2B
Posts: 82
Joined: Fri Sep 29, 2017 7:07 am
Been upvoted: 1 time

### Re: entropy of heavy vs. light molecules

I think a partial answer could stem from what Dr. Lavelle mentioned in class about the element with more electrons having greater entropy because there are more possible positions of the electrons. I think the same can be applied to your question ... if there is a heavy and light version of a similar object, the heavier version has greater entropy due to the more possible combinations. Something else important to note about entropies is that entropies of large, complicated molecules are greater than those of smaller, simpler molecules.

Chris Lamb 1G
Posts: 58
Joined: Fri Jun 23, 2017 11:39 am

### Re: entropy of heavy vs. light molecules

Molecules with more "parts," such as electrons, protons, and other atoms bonded, have more possible orientations and vibrations than simpler molecules. This means they have more entropy.