Hi, Claire,
The heat of soultion is the energy involved in dissolving a solute in water. The value of 22.59 kJ/mol for silver nitrate tells us that 1 mole of silver nitrate requires 22.59 kJ to dissolve in water. This energy is often taken from the water, since it is blessed with a high specific heat and has plenty of energy to share. The net result is the solution will undergo a temperature drop as the energy is removed from the water. A nearby chemist would characterize this dissolution of silver nitrate as endothermic.
Bob
