[Freezy]

I am trying to create a cooling effect and found that dissolving urea and ammonium chloride in water creates a significant chilling effect. I was wondering what the products of this reaction are and if it can be reversed if the water is evaporated out of it.

[Arkcon]

Those solids are known to have a negative heat of solution: https://en.wikipedia.org/wiki/Enthalpy_change_of_solution#Dependence_on_the_nature_of_the_solution  (the ones with + in that table)  And yes, when the water is evaporated, these particular chemicals don't change, so it can be done again.