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

1. Feb 9, 2004

Silverious

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. Feb 9, 2004

Silverious

I've thought about the first question a bit more.

Is $$\frac{lnP_2 - lnP_1}{\frac{1}{T_2} - \frac {1}{T_1}} = - \frac{\Delta H}{R}$$ what I'm looking for?

3. Feb 9, 2004

Silverious

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. $$V_{unit cell} = \frac {m_{unit cell}}{d}$$

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 $$\frac {\sqrt{3}s}{4} = r$$.

4. Feb 12, 2004

Silverious

Is no one going to reply to this? Or should I post these in chemistry forum?

5. Feb 12, 2004

Bystander

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