Why is mixing water with potassium chloride an endothermic process?

1 Answer
Oct 1, 2015

Because strong electrostatic bonds between oppositely charged ions are disrupted upon dissolution.


#KCl(s) rightleftharpoons K^+(aq) + Cl^-##(aq)#

Dissolution disrupts the strong electrostatic bonds between the oppositely charged ions of the lattice. Bond breaking requires energy, and therefore, the reaction is endothermic. The individual ions are aquated by water molecules (which is why we write #K^+(aq)#), but such bond formation does not energetically compensate for the initial bond breaking.