Question

te the lattice energy for LiF(s) given the following:

sublimation energy for Li(s)	+166 kJ/mol
∆Hf for F(g)	+77 kJ/mol
first ionization energy of Li(g)	+520. kJ/mol
electron affinity of F(g)	–328 kJ/mol
enthalpy of formation of LiF(s)	–617 kJ/mol

	A.	none of these
	B.	–650. kJ/mol
	C.	285 kJ/mol
	D.	800. kJ/mol
	E.	1052 kJ/mol

Answer 1

We know that

enthalpy of formation of LiF(s) = sublimation energy for Li(s) + first ionization energy of Li(g) + ∆H_f for F(g)

                                                    + electron affinity of F(g) + lattice energy for LiF(s)

So lattice energy for LiF(s)

= enthalpy of formation of LiF(s)-( sublimation energy for Li(s) + first ionization energy of Li(g) + ∆H_f for F(g)

                                                    + electron affinity of F(g) )

= -617 -(+166 +520 +77 +(-328))

= -1052 kJ/mol ( -ve sign indicates that heat is released)

So the lattice energy is 1052 kJ/mol

Therefore option (E) is correct