So Ag+ + Cl- ---> AgCl and delta H is -65.5 kJ. I'm supposed to calculate delta H when one mole of AgCl dissolved in water, so 1 mol AgCl *(65.5 kJ/1mol Agcl) right? But the answer is 65.5 kJ, and why is it positive, not negative, is my question.

Answer 1

Ag^+ + Cl^- ==> AgCl dH= -65.5
so AgCl ==> Ag^+ + Cl^-, the reverse of what is -65.5 gives you +65.5 kJ/mol.

Answer 2

I think it's becos it's a formation reaction enthalpy is always: -deltaH:-1*-65.5=65.5KJ

Answer 3

Yes, it is a dHo (formation) which is the reverse of what you want.