Consider the Born-Haber cycle for the calculation of the lattice energy of calci

Question

Consider the Born-Haber cycle for the calculation of the lattice energy of calcium chloride.

1.) Enter the chemical equation for the overall reaction: the formation of calcium chloride from its constituent elements in their standard states.Include all phases.

2.) Enter the chemical equation for the formation of the gaseous metal from its standard state. Include all phases.

3.) Enter the chemical equation for the dissociation of the gaseous diatomic nonmetal. Include all phases.

4.) Enter the chemical equation for the ionization of the gaseous metal atom. Include all phases.

5.) Enter the chemical equation for the electron addition to the gaseous nonmetal atoms. Include all phases.

6.) Enter the chemical equation for the formation of the crystalline solid from the gaseous ions. Include all phases.

7.) Which of the above reactions has an enthalpy that corresponds to the lattice energy?

Explanation / Answer

(1) Ca (s) + Cl2 (g) -----------> CaCl2 (s) , deltaH1 = - 795.0 kJ

(2) Ca (s) ---------> Ca (g) deltaH2 = + 178 kJ

(3) Cl2 (g) ----------> 2 Cl (g) , deltaH3 = + 242 kJ

(4) Ca (g) ----------> Ca2+ (g) , deltaH4 = 1735 kJ

(5) 2 Cl + e ------------> 2 Cl-, deltaH5 = - 728kJ

(6) Ca2+ (g) + 2 Cl- (g) ------------> CaCl2 (s), deltaH6 = ?

(7) step (6) corresponds to lattice enrgy.

According to Hess law,

deltaH1 = deltaH2 + deltaH3 + deltaH4 + deltaH5 + deltaH6

- 795 = + 178 + 242 + 1735 - 728 + L.E

L.E = Lattice Energy = - 2225 kJ

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