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Homework Help: Clausius-Clapeyron Equation, and Cubic Unit Cells

  1. Feb 9, 2004 #1
    1. Acetone has normal boiling point of 56.5 oC, and heat of vaporization of 32.0 kJ/mol. Find the boiling point at 580 mmHg.

    2. Given element, its structure and density, find its atomic radius in pm. Cr, body centered cubic, 7.19 g/mL.

    Well, as for question 1, I'm totally stumped. Everytime I try to go about doing any problem like this, my brain locks up. I think I just don't have a firm understanding of the idea.

    Number 2, well, umm...again, same as above. I really just don't understand anything. It's pretty frustrating. So if someone could help me pleaseeeee, I will become their slave.
  2. jcsd
  3. Feb 9, 2004 #2
    I've thought about the first question a bit more.

    Is [tex] \frac{lnP_2 - lnP_1}{\frac{1}{T_2} - \frac {1}{T_1}} = - \frac{\Delta H}{R} [/tex] what I'm looking for?
  4. Feb 9, 2004 #3
    I'm not crazy, talking to myself am I?

    Anyways, regarding the second question.

    First I have to determine the mass of a single unit cell.

    I believe, this is found by determining the molar mass of Cr, then converting it to amu's. Since there are 2 nuclei in a body centered cubic cell, it would be 2x Molar Mass(in amu) correct?

    Now, in order to determine the actual radius, I need to use density fomrula. [tex] V_{unit cell} = \frac {m_{unit cell}}{d} [/tex]

    But first I convert mL into cubic whats? I forget...oh well. Anyways, from there, I convert to picometers, then I take the cube of this number, which is "s". But I can't use this yet. Sooooo, I use [tex] \frac {\sqrt{3}s}{4} = r [/tex].

    Someone please verify these?
  5. Feb 12, 2004 #4
    Is no one going to reply to this? Or should I post these in chemistry forum?
  6. Feb 12, 2004 #5


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    You're doing fine --- you got the concepts --- at that point, it becomes an exercise in arithmetic.
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