Exercise 19.38b solutions manual & MC

[Zellmer, Robert]

Someone asked about 19.38b.  This is and end-of-chapter exercise
and is in the MC homework.  This problem states "If you heat a gas
such as CO2, you will increase its degrees of translational, rotational
and vibrational motions."  True or False.

The solutions manual states "False".  MC states this is "True".

The problem really is the question was worded poorly.  The fact is
the degrees of freedom (or number of them) themselves don't change.
They are what they are.  The added heat will be distributed between
more of these motions.  Remember the figure of the fraction of molecules
with some kinetic energy versus kinetic energy.  As the temp rises the
distribution of molecules shifts to the right and spreads out.  This
spreading out of the distribution results in more microstates for the
translational motions.  This added heat causes more rotations of the
molecules and inc. the vibrational motions.  Adding heat causes them
to move around more, rotate more and the bonds w/in a molecule to
vibrate more. This leads to more microstates.  You can see pictures in
the solutions manual (although the picture leaves out 1 rotational motion
and 1 vibrational motion).

Here's a link to a discussion of vibrational degrees of freedom in general.

https://chem.libretexts.org/Textbook_Maps/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Spectroscopy/Vibrational_Spectroscopy/Vibrational_Modes/Number_of_Vibrational_Modes_in_a_Molecule <https://chem.libretexts.org/Textbook_Maps/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_%28Physical_and_Theoretical_Chemistry%29/Spectroscopy/Vibrational_Spectroscopy/Vibrational_Modes/Number_of_Vibrational_Modes_in_a_Molecule><https://chem.libretexts.org/Textbook_Maps/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_%28Physical_and_Theoretical_Chemistry%29/Spectroscopy/Vibrational_Spectroscopy/Vibrational_Modes/Number_of_Vibrational_Modes_in_a_Molecule>

Also, this goes to how microwave ovens work.  The electromagnetic radiation
produced by the microwave oven causes the molecules to rotate and the bonds
to vibrate.  These motions cause the molecules to heat up causing the food to
be heated.  The water content plays a big role in how the food heats.  Here's some
links explaining this.  Interestingly enough the first food cooked in a microwave
oven was popcorn.

https://en.wikipedia.org/wiki/Microwave_oven

https://van.physics.illinois.edu/qa/listing.php?id=821

https://www.explainthatstuff.com/microwaveovens.html

Dr. Zellmer
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osu.edu/pipermail/cbc-chem1220/attachments/20220329/a62addba/attachment-0001.html>