Question

The dissolution of ammonium chloride in water is ENDOTHERMIC, and yet ammonium chloride is VERY soluble in water. Why so?

Answer 1

Because the driving force of chemical change is not enthalpy, but ENTROPY.

Explanation:

Entropy, the statistical probability for disorder, increases in every spontaneous chemical reaction. And a dissolution reaction is certainly accompanied by an increase in entropy.

And thus.....

`NH_4Cl(s) + Delta rarrNH_4^+ + Cl^-`

....while endothermic, gives rise to solvated ions that increase the disorder of the system.

And of course, for some dissolution reactions, the enthalpy term dominates....

`AgCl(s) rightleftharpoonsAg^+ + Cl^-`

And of course silver chloride is as a soluble as a brick, and this reflects the strength of the ionic bond between the halide and the metal.