By convention, the lattice energy is the energy required to break up one mole of
ID: 921130 • Letter: B
Question
By convention, the lattice energy is the energy required to break up one mole of a solid ionic compound into its gaseous ions. Since we cannot directly measure lattice energies, we generally use the Born-Haber cycle to calculate the lattice energy from other measurable quantities. For instance, the Born-Haber cycle of sodium chloride is shown below.(Figure 1) In this cycle, the lattice energy is calculated using the enthalpy of formation of sodium chloride, ?H?f[NaCl(s)], the enthalpy of formation of gaseous chlorine, ?H?f[Cl(g)], the first ionization energy of sodium, I1(Na), and the electron affinity of chlorine, E(Cl).
Given the following thermodynamic data, calculate the lattice energy of CaBr2(s).
Value (kJ mo Ii(Ca) I2 (Ca) E(Br) 179 112 590 1145 -325 Express your answer as an integer, and include the appropriate units. AHlatt 2051 kJ Submit Hints My Answers Give Up Review Part Incorrect; One attempt remaining; Try AgainExplanation / Answer
Hf(CaBr2) = Datomisation(Ca) + I1(Ca) + I2(Ca) + 2 X Datomisation(Br2) + 2 X EA(Br) + Lattice Energy(CaBr2)
So -675 = +179+590+1145+(2 X 112)+(2 X -325)+L.E.(CaBr2) (All units in kJ mol-1 )
So L.E.(CaBr2) = -675-179-590-1145-224+650 = -2163 kJ mol-1
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