The enthalpy changes, ΔH  , for three reactions are given.

H  2 (g)+12 O  2 (g)Ca(s)+2H + (aq)CaO(s)+2H + (aq) ⟶H  2 O(l)⟶Ca 2+ (aq)+H  2 (g)⟶Ca 2+ (aq)+H  2 O(l) ΔH=−286 kJ/molΔH=−544 kJ/molΔH=−193 kJ/mol  

Using Hess’s law, calculate the heat of formation for CaO(s)  using the reaction shown.

Ca(s)+12 O  2 (g)⟶CaO(s) 

Answer in kJ/mol