Calculate the lattice enthalpy for lithium fluoride, given the following informa

Question

Calculate the lattice enthalpy for lithium fluoride, given the following information: o Enthalpy of sublimation for solid lithium 161 kJ/mol o First ionization energy for lithium 520 kJ/mol F-F bond dissocation energy 1,54 kJ mol or Enthalpy of formation for F(g)-77 kJ/mol o Electron affinity for fluorine 328 kJ/mol Enthalpy of formation for solid lithium fluoride =-617 kJ/mol Use the following information to calculate the heat of sublimation for potassium: Heat of formation for KCI(s)- -437 kJ/mol Electron affinity for Cl =-349 kJ/mol Ionization energy for K = 418 kJ/mol Lattice energy for KCl = 717 kJ/mol -7 o o o Heat of formation for Cl(g)-122 kJ/mol or Bond dissociation energy for Cla(g) 243 kJ/mol

Explanation / Answer

According to Hess law,

dHf = dHs + dHIe + dHf of F + dHea + dH Lattice energy

dHf = enthalpy of formation

dHs = sublimation energy of Li

dHIe = ionization energy of Li

dHf of F = enthalpy of formation of F

dH ea = electron affinity of F

from the given data,

-617 = 161 + 520 + 77 +(-328) + dH lattice

dH lattice energy = -1047 kJ/mol

Hence lattice energy of LiF = 1047 kj/mol

According to Hess law,

dHf = dHs + dHIe + dHbd + dHea + dH Lattice energy

dHf = enthalpy of formation

dHs = sublimation energy of K

dHIe = ionization energy of K

dHf of Cl = enthalpy of formation of Cl

dH ea = electron affinity of Cl

from the given data,

-437 = dHs + 418 + 122 + (-349) + (-717)

dHs = 89 kJ/mol

Here we have to consider lattice energy as negative value because the crystal is formed from its gaseous ions hence the energy is released. so lattic enrgy is value in dH terms = -ve

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