[Noofer]

Is there any chemical with a highly positive  :delta:rH in kJg^-1?

[UG]

Photosynthesis?

[Noofer]

Yes that is true, although I was more looking for an application where an endothermic reaction could cool down a gas quickly by extracting the heat energy from it, where photosynthesis wouldn't be practical.

[typhoon2028]

Can the gas be expanded through a valve?

[Noofer]

Yes, that would be possible

[typhoon2028]

Can you utilize the joule-thompson effect?

[marquis]

The one used in ice packs is ammonium nitrate as it dissolves in water. 

Is that good enough?

[Ajax Warwick]

I think about a flame of fire it is a endo or esothermic reaction endo-> since to start, the reaction needs to waste air, then power eso-> since the fire produces heat, so it externalise the power.



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[Noofer]

Hmmmm, Joule-thomson effect is an interesting concept. Although I was more looking for something as an alternate form of cooling, instead of having the need for electricity to power a compressor.

Ammonium Nitrate is a point, didn't think of that. Thank you for that suggestion.

A flame is an exothermic reaction as it is created by a chemical reaction which releases energy to it's environment, causing the heat and plasma. So it wouldn't really be what I was meaning.

Thank you all for your suggestions.