# Thermodynamics triple point

whitewanderer
This is my first post, and I am lost in this thermodynamics question. The question is as follows:

The equations of the sublimation and the vaporization curves of a particular material are given by

ln P = 0.04 -6/T (sublimation)
ln P = 0.06 - 4/T (vaporization)

where P is in atmospheres.

a) find the temperature of the triple point.
b) show the specific lateant heats of vaporization and sublimation are 4R and 6R respectively
c) Find the latent heat of fusion.

Can anyone give me somewhere to start on this problem? The problem is in the Thermodynamic Potential chapter, so I am assuming I should use the Helmholtz or the Gibbs function somehow. Any help would be awesome!

Thanks

whitewanderer

## Answers and Replies

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Show us what you've got so far on "a)" --- might as well start there as anywhere.

whitewanderer
I tried setting them equal, but that gave me some odd decimal point answer, and I don't think that's right. I'm basically stuck at where to go. I don't see how I can use any potential equations to get a triple point. I can see for b where the 4R and the 6R come from (obviously the term with 1/T in it) but not sure where to go from there for the second part. The third part is just like the first, where I don't know where to go with it. It's so confusing!

whitewanderer

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Originally posted by whitewanderer
I tried setting them equal, but that gave me some odd decimal point answer, and I don't think that's right.

Something in particular "wrong" with an "odd decimal point answer?"

I'm basically stuck at where to go. I don't see how I can use any potential equations to get a triple point.

Look for "van 't Hoff" in your text index.

I can see for b where the 4R and the 6R come from (obviously the term with 1/T in it) but not sure where to go from there for the second part. The third part is just like the first, where I don't know where to go with it.

See "Hess's Law."
It's so confusing!

whitewanderer

I will suggest that as much effort be put into reading and review of class notes as was put into evading a straight answer to what you've accomplished on "a)" --- YOU'RE the one coming here for help --- you don't cooperate with some description of what you've done, can do, and are willing to do to learn, this can turn into a very frustrating experience.

"van 't Hoff" and "Hess's law" are the legal limit for hints on this.

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Okay, gang, this is how NOT to use the help forums:
this thread began in General Physics and was moved to K-12?

Originally posted by whitewanderer
This is my first post, and I am lost in this thermodynamics question. The question is as follows:

The equations of the sublimation and the vaporization curves of a particular material are given by

ln P = 0.04 -6/T (sublimation)
ln P = 0.06 - 4/T (vaporization)

Anyone see anything "funny" yet? It's there. RULE ONE: double check your transcriptions of problems to the forums.
where P is in atmospheres.

a) find the temperature of the triple point.
b) show the specific lateant heats of vaporization and sublimation are 4R and 6R respectively
c) Find the latent heat of fusion.

Can anyone give me somewhere to start on this problem?

RULE TWO: read Tom's guidelines for posting to HW help.
The problem is in the Thermodynamic Potential chapter, so I am assuming I should use the Helmholtz or the Gibbs function somehow. Any help would be awesome!

Thanks

whitewanderer

Solving a system of two equations in two unknowns is trivial; when asked for specifics of what isn't intuitively satisfying, or seems "wrong" with the solution, don't disappear from the forum, state your case --- someone will be more than happy to tell you that what's wrong with the "odd decimal point answer" is that it includes a negative value for the thermodynamic temperature scale --- please check the original problem statement.

You want thermo help? Ask for it. You want thermo help AND "milk and cookies?" Dream on.

I have PM ed ww re MY lack of patience.