What is the strongest endothermic reaction involving salt and liquid water?

AI Thread Summary
The discussion centers on finding a dissolution process of a salt that produces the largest temperature drop and absorbs significant energy from its surroundings, specifically over 1000 J/g for refrigeration purposes. The most effective option identified is ammonium nitrate, which absorbs 403 J/g upon dissolution. However, this is still below the desired threshold. The conversation highlights the challenge of finding highly endothermic reactions, noting that many salts, like sodium hydroxide, release heat instead. A commercial solution involves ammonium nitrate encapsulated in a bag that cools when mixed with water. Additionally, the discussion mentions a chemical demonstration using ammonium nitrate and barium hydroxide, which also produces a cooling effect. Other endothermic processes, such as evaporation, are acknowledged but do not meet the specific requirements for energy absorption in this context.
Alistair1992
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Hi,

I'm looking for the reaction that produces the largest temperature drop/absorbs the most energy from its surroundings. It needs to be some kind of dissolution process of a salt being mixed with liquid water. I've looked around on the internet, and it seems tricky to search for, and I don't know much about chemistry (being an engineer), so am struggling to calculate it from theory.

Thanks,

Alistair
 
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I would start with CRC handbook or something similar - I doubt you will find much better choices than those already known and listed.
 
Thanks. I've looked, and the strongest one I can find absorbs 403J/g from its surroundings. Ideally, I was looking for something over 1000 for a refrigeration idea.
 
Hard to find highly endothermic reactions, as for spontaneity they need a huge entropic factor (ΔG=ΔH-TΔS > 0). Perhaps something with a gaseous product could work, but simple dissolution doesn't sound likely to me.
 
There are commercial products available that do this. Ammonium nitrate salt is encapsulated in an inner plastic bag inside a second bag with water. Breaking the inner bag mixes the salt and water, and cools off. This salt has an enthalpy of solvation that is smaller than the enthalpy of crystallization. Many salts (e.g. NaOH) are the opposite -- i.e. they release heat upon dissolution.

c.f. http://www.pleasanton.k12.ca.us/avhsweb/cutter/Chemistry/Portfolio_files/Hot&ColdPacks.pdf

There is a common chemical demonstration where you freeze a flask to a bit of wood, using a reaction between ammonium nitrate and barium hydroxide.



Other spontaneous endothermic processes (evaporation -- think sweat and evapotranspiration)
 
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Quantum Defect said:
Ammonium nitrate

325 J/g, three times less than OP asks for.
 
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