. Write a chemical equation that goes with Lattice energy of CaCl 2 (s). Solution 1. i. Sublimation of Ca Ca (s) --------> Ca (g) , deltaH 0 sub ii. Ionisation of Ca to Ca 2+ Ca (g) -----------> Ca 2+ (g) + 2 e - , deltaH 0 IE iii. Dissociation of Cl 2 Cl 2 (g) -----------> 2 Cl (g), deltaH 0 b iv. Elctron gain enthalpy of Cl Cl (g) + e - ----------> Cl - (g) , deltaH 0 EA v. Lattice energy Ca 2+ (g) + 2 Cl - (g) -----------> CaCl 2 (s) , U 2. Over all reaction of formation of CaCl 2 is, Ca (s) + Cl 2 (g) -----------> CaCl 2 (s) , deltaH 0 r Accroding Hess,s\' law, deltaH 0 r = deltaH 0 sub (Ca) + deltaH 0 IE (Ca) + deltaH 0 b (Cl 2 ) + 2 * deltaH 0 EA (Cl) + U Therefore, U = lattice energy = deltaH 0 r - deltaH 0 sub (Ca) - deltaH 0 IE (Ca) - deltaH 0 b (Cl 2 ) - 2 * deltaH 0 EA (Cl) .