Lattice energy = -820 kJ/mole
Heat of solution = +22.6 KJ/mole
Lattice breakdown is and endothermic reaction during the formation of solution
And hydration is an exothermic reaction as ions interact with solvent molecules
By using the formula,
Enthalpy of solution = Lattice energy + hydration energy
Now put the values and calculate,
+22.6 kj/mole = + 820 kj/mole + hydration energy
Hydration energy = 22.6 Kj/mole – 820 Kj/mole
Hydration energy= -797.4 Kj/mole