Calculate the lattice energy for CaCl 2 from the following information: Energy n

Question

Calculate the lattice energy for CaCl2 from the following information: Energy needed to vaporize one mole of Ca(s) is 192kJ. For calcium the first ionization energy is 589.5kJ/mol and the second ionization energy is 1146kJ/mol. The electron affinity of Cl is -348kJ/mol. The bond energy of Cl2 is 242.6kJ/mol of Cl-Cl bonds. The standard heat of formation of CaCl2 is -795kJ/mol. ( include the sign and your numerical answer, do not include units, do not use scientific notation, and round your answer to 1 decimal point)   

Explanation / Answer

ca(s) + cl2(g) ______ Cacl2 now deltaHf = - 795 kj/mol
total ionisation enthalpy = 589.5 + 1146 = 1735.5 kj/mol
sublimation enthalpy = 192 kj/mol
total bond dissociation enthalpy = 242.6 kj/mol
we have two cl atoms so electron gain enthalpy for two atoms is = 2*(-348) = -696 kj/mol as electron gain enthalpy = -(electron affinity)

so using born haber cycle
enthalpy of formation = enthalpy of sublimation + ionisation enthalpy + bond dissociation enthalpy + electron gain enthalpy + lattice enthalpy
-795 = 1735.5+192+242.6-696+lattice enthalpy
so lattice enthalpy = -795 - 1474.1 = - 2269.1 kj/mol

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