Construct a Born-Haber cycle andcalculate the lattice energy of CaC2 (s). Note t

Question

Construct a Born-Haber cycle andcalculate the lattice energy of CaC2 (s). Note that thissolid contains the diatomic ionC2^2-
Useful Information: H°f(CaC2(s)) = –60 kJ/mol Hsub (Ca (s)) = +178kJ/mol Hsub (C (s)) = +717kJ/mol Bond dissociation energy of C2 (g) =+614 kJ/mol First ionization energy of Ca (g) =+590 kJ/mol Second ionization energy of Ca (g) =+1143 kJ/mol First electron affinity of C2 (g) =–315 kJ/mol Second electron affinity of C2 (g) =+410 kJ/mol Construct a Born-Haber cycle andcalculate the lattice energy of CaC2 (s). Note that thissolid contains the diatomic ionC2^2-
Useful Information: H°f(CaC2(s)) = –60 kJ/mol Hsub (Ca (s)) = +178kJ/mol Hsub (C (s)) = +717kJ/mol Bond dissociation energy of C2 (g) =+614 kJ/mol First ionization energy of Ca (g) =+590 kJ/mol Second ionization energy of Ca (g) =+1143 kJ/mol First electron affinity of C2 (g) =–315 kJ/mol Second electron affinity of C2 (g) =+410 kJ/mol

Explanation / Answer

Hsub (Ca (s)) = +178kJ/mol              Ca(s) -> Ca(g)
Hsub (C (s)) = 2*+717kJ/mol             2C(s) ->   2C(g)
-BDE of C2 (g) = - 614kJ/mol              2C(g) ->   C2(g)
First IE Ca (g) = +590kJ/mol                Ca(g) -> Ca+(g)
Second IE Ca (g) = +1143kJ/mol          Ca+ (g) -> Ca2+ (g)
First EA of C2 (g) = –315kJ/mol            C2 + e- -> C2-
Second EA C2 (g) = +410kJ/mol          C2- + e- -> C2^2-

Sum above = 2826 kJ/mol           for Ca(s) + 2C(s) => Ca2+ (g)   +  C2^2-              Eqn 1

Lattice Energy is for reaction,    Ca2+ (g) + C2^2-(g) => CaC2(s)                                Eqn 2

Adding equation 1 and 2 yields Ca(s) + 2C(s) => CaC2(s), which has H = -60 kJ/mol

So lattice energy = -60 - (2826) = -2886 kJ/mol

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