NH4NO3 and cons. of energy

[El_Zorro]

This question really has nothing to do with clandestine chemistry directly, but I've always wondered why ammonium nitrate cools down when it's added to water.  See, you have to heat NH₄NO₃ to drive off the water, but when you do this to other hygrosopic compounds, when water is added to them, heat is given off, which equals the amount of heat needed to drive off the water, in accordance to the law of conservation of energy.  Compouds in question, NaOH, and Copper(II) Sulfate(all I can think of off the top of my head).  So why does NH₄NO₃ absorb heat when it's added to water?  Wouldn't this mean that it is capable of absorbing an infinite amount of heat?

Anyway, just a bored bee's musings.
Zorro

[Elementary]

Apparently it's all to do with entropy !

Here are some explaining links

http://www.chemistry.mcmaster.ca/~aph/chem1a3/lectures/lec03/sld016.htm

http://www.2ndlaw.com/entropy.html

One day I'll understand everything !

[El_Zorro]

I still don't get it.   It still seems to me that NH₄NO₃ should be able to absorb an infinite amount of heat through repeated drying/wetting.
Zorro

[PolytheneSam]

That's the example that my P. Chem. teacher used to demonstrate that not all spontaneous chemical reactions are exothermic (this one's endothermic).  Apparently, when you heat it, it doesn't absorb the ("heat") energy of hydration, but gives it off, thus conserving energy.  After the demonstration the teacher began lecturing about Gibb's free energy and chemical potential.  The change in chemical potential is the change in Gibb's free energy per mole.  Before you get to that study the Carnot cycle.
http://www.geocities.com/dritte123/PSPF.html

[foxy2]

Think of it this way, NH4NO3 is homosexual and the others are heterosexual. (wrt H2O)



When you figure out what I just said it will all make sense.

Fully Informed Jury!

(http://www.fija.org/)

[PolytheneSam]

Here's a good book for you.

http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=1509099872

http://www.geocities.com/dritte123/PSPF.html

[PolytheneSam]

I was thinking about this thread and wondered why the answer isn't obvious to everyone.  Heat of hydration isn't in my P. Chem. book but I found this.  Its heat of solution which is related.  Here's one example:

HCl(g) + H2O(l) = HCl in 5H2O ; change in enthalpy is -64.06 kJ/mol

The - sign means its exothermic and the reaction is reversible.  With ammonium nitrate the sign would be + when going from the anhydrous state to the hydrated state and - when going back.
http://www.geocities.com/dritte123/PSPF.html

[El_Zorro]

Hmmmmmmmmm...................
Zorro

[SilverSurfer]

What my previous speakers wanted to say    is the energy that u need to resolve the ionic bonds
in the cristal-grate is bigger than the energy that is provided by the H2O Dipols when they arrange them
round the NH4+ NO3- Ions. The reason for this process is like said above the entropie.

[El_Zorro]

Oh shit!! It hits me in brief clarity!!

So let's see if I got it right.  The water molecules arrange themselves around the NH₄NO₃ crystalline structure, but do not have the energy to break the bonds.  So they draw energy in the form of surrounding heat to break the bonds.  And when heat is added to drive off the water, the water leaves, but there is also the added heat that had been absorbed to break the ionic bonds, and that is released along with the water, conserving energy.

Zorro

[halfapint]

Anybody beesides me ever tried to use the catalyzed breakdown of ammonium nitrate to oxidize alkene to carbonyl? Works wonders when the reagent goes away as nitrogen --- should generate an oxidant transfer species in DMSO, maybee acetone. After US 3965185, which PolySam still has wrong on his web site. The patent sez acidic conditions are needful, unfortunately for asarone. (In acetic acid asarone --> gum.)  Expect it gen's peroxyacids, like H2O2 would, from acetic, formic, benzoic acids etc., not sure tho.
a half a pints a half a pound a half a world a half a round
demimonde, n. Half world.

[Rhodium]

Correct. That's why ammonium nitrate crystallizes so nicely, as the crystallization is exothermic (thereby the crystallization forces itelf to be slow). Forming 10 cm long crystals does not take any effort at all.



Note that it is a 2000ml flask in the pic, so many of the needles are over 15cm long, and formed spontaneously from a hot solution upon cooling. Sorry for the bad image quality.

[PolytheneSam]

US patent 3965185 is listed at

http://www.geocities.com/dritte123/Miscpat.html

and its on Pd Wacker with NH4NO3 maintains catalyst active for continuous conversion of olefin to carbonyl compound just like it says.

http://www.geocities.com/dritte123/PSPF.html

[halfapint]

Oh, must have had an old page still in my cache. Pd isn't necessary at all; works with iron salts, and I have successfully used nickelous chloride as catalyst.
a half a pints a half a pound a half a world a half a round
demimonde, n. Half world.

[El_Zorro]

I never have been able to get anything unless I can picture it in my head.  I don't know.  Maybe I should train myself to understand more abstract concepts, if that is really possible.

Rhodium-Did you have that picture laying around, or did you xtallize that just for me?
I sell crack for the CIA

[Rhodium]

Actually, I did that particular recrystallization because of inspiration from this thread, and as I had those nice crystals in the flask anyway, I thought why not post them?

[El_Zorro]

Those are some pretty sexy crystals
I sell crack for the CIA