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May 22, 2015

Homework Help: Chemistry

Posted by Christopher on Thursday, March 22, 2007 at 7:13pm.

Given the following information about xenon
normal boiling point = -108 degrees C
normal melting point = -112 degrees C
triple point = -121 degrees C at 281 mmHg
critical point = -16.6 degrees C at 58 atm

a) Construct an appropriate phase diagram for xenon [I did this.]
b) Estimate the vapor pressure of xenon at -115 degrees C.
c) Is the density of solid Xe larger than that of liquid Xe?

For b, I figured I could solve the problem with the Clausius-Clapeyron equation if I was provided with the heat of vaporization. However, I'm not, and I'm not sure that I'd be able to find it with the information given. How can I solve the problem with this information?

For c, should this be done qualitatively or is it not possible [with the info given]/ not necessary? I had written down that yes, solid Xe is more dense than liquid Xe because the solid would always be more dense than its liquid [is this a false assumption?].

For b, look in your text or notes on phase diagrams. The phase diagram will allow you to estimate vapor pressure at any temperature.
For c. you have made a false assumption. Ice, for example, is less dense than water (that's why ice floats). Again, the phase diagram will tell you about the density of the solid. Phasd diagrams consist of three parts. The lower part which is curved slightly upward from below freezing to the freezing point, starting there another section which goes up and above the boiling point, and a third line which is almost vertical that starts at the freezing point and points upward. If the slope of the nearly vertical line is negative, the solid is less dense than the liquid. If the slope of that nearly vertical line is positive, the solid is more dense than the liquid. I hope this helps. The solution to this problem is to understand phase diagrams.

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