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I am not a chemist. But I am curious...

This evening I was making ingredients for a "lemonade bar", where people mix various flavors into a lemonade base to create custom flavors (mint + cucumber is a favorite, strawberry + ginger is another).

I wanted to offer "really sour" as one of the mix-ins, so I put about an ounce of food-grade powdered citric acid in a jar and added enough apple juice to make it dissolve [see note]. I shook it vigorously, and as the citric acid dissolved, I noticed that the jar got fairly cold.

That's neat! So what's the process that makes apple juice + citric acid get cold?

(For extra credit: are there other kitchen counter endo- or exo-thermic reactions I should try with my six year old son?)

update

I just repeated the experiment mixing tap plain water and citric acid. It was also endothermic, dropping the water temperature from 21.5 to 11.5 celsius.

[note] And yessir, it's really sour! :)

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    $\begingroup$ Breaking up the lattice of the solid citric acid costs energy. That energy is taken from the solvent. Same reason that water gets colder if you add salt $\endgroup$ – Fl.pf. Apr 21 '17 at 10:50
  • $\begingroup$ Dissolving ammonium nitrate is quite endothermic, and is used in cold packs, e.g. for athletic injuries. $\endgroup$ – DrMoishe Pippik Apr 21 '17 at 19:47

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