Heat of solution of BaCl2.2H2O - 200 kJ mol-1Heat of hydration of BaCl2 = - 150 kJ mol-1Hence heat of solution of BaCl2 is

We have BaCl2⋅2H2O+aq→Ba2+(aq)+2Cl−(aq)+2H2O;ΔH=200kJmol−1BaCl2+2H2O→BaCl2⋅2H2O;ΔH˙=−150kJmol−1On adding both equation we getBaCl2+aq→Ba2+(aq)+2Cl−(aq) ΔH=50kJmol−1This is the reaction for dissolution of BaCl2. Therefore heat of this reactions is in fact the heat of solution of BaCl2.