Calculate heat of solution of NaCl from the following data
Hydration energy of Na⁺ = –389kJ mol^–1
Hydration energy of Cl^– = –382kJ mol^–1
Lattice energy of NaCl = +776 kJ mol^–1

Hydration energy of NaCl = Hydratin energy
of Na⁺ + Hydration energy of Cl^–
= – 389 – 382 = – 771kJ/mol
Heat of solution = Hydration energy – Lattice energy
= [–771– (–776)] = 5kJ / mole