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<div class="moz-cite-prefix">On 01/26/14 14:37, <br>
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<div style="margin-top: 0px; margin-bottom: 0px;">Dr. Pounds,</div>
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<div style="margin-top: 0px; margin-bottom: 0px;">I've been
reading the chapter and working the checkpoints and I got most
of them correct. I started working on the homework and I'm
still confused on a few things. I understand that compounds
that have low boiling points will have high vapor pressures.
But I don't understand how you can tell one compound has a
higher boiling point than another compound. I am also confused
about the concepts you have to understand to be able to answer
number 136.
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<div style="margin-top: 0px; margin-bottom: 0px;">Thank you for
your help,</div>
<div style="margin-top: 0px; margin-bottom: 0px;"><br>
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<br>
Problem 136 from Burdge and problem 14 from the chapter 11
additional problems are on my list to do tomorrow in class.<br>
<br>
As far as how to tell which molecule has the higher boiling, it is
ALL tied to the intermolecular forces involved (section 11.1 in
Burdge). Except for blatantly obvious questions, like which has
the higher boiling point, H<img style="vertical-align: middle"
src="cid:part1.02010007.05030302@mercer.edu" alt="$_2$"> or H<img
style="vertical-align: middle"
src="cid:part1.02010007.05030302@mercer.edu" alt="$_2$">O, you
really have to conceptualize the three dimensional molecular
structure. In other words, you have to think about the Lewis
diagram and how that translates to a 3D molecular shape (VSEPR
theory, section 9.1 in Burdge, CHM 111 stuff). Once you do that
then you should determine if there is a dipole moment present
(section 9.2 in Burdge).<br>
<br>
Here are some simple rules that I follow when comparing two
molecules:<br>
<br>
1. the molecule with the most intermolecular forces will have the
higher boiling point.<br>
<br>
2. if two molecules have the same number of intermolecular forces<br>
a) the one with the stronger intermolecular forces will have the
higher boiling point<br>
b) if comparing polarity, the molecule with the more
electronegative atom will have the higher boiling point<br>
c) if all of the forces are the same, then the heavier molecule
will have the higher boiling point<br>
<br>
<br>
I just took a look at the book and sample problem 11.1 on page 481,
the subsequent three practice problems, and numerous end of chapter
review problems (11.1 - 11.21) do a good job driving these points
home.<br>
<br>
<pre class="moz-signature" cols="72">--
Andrew J. Pounds, Ph.D. (<a class="moz-txt-link-abbreviated" href="mailto:pounds_aj@mercer.edu">pounds_aj@mercer.edu</a>)
Professor of Chemistry and Computer Science
Mercer University, Macon, GA 31207 (478) 301-5627
<a class="moz-txt-link-freetext" href="http://faculty.mercer.edu/pounds_aj">http://faculty.mercer.edu/pounds_aj</a>
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