determine lattice energy given this information?

Question

I need assistance determining the lattice energy for the compound MX2 given the following information: The enthalpy of formation of MX2 is ΔHf° = –759 kJ/mol. The enthalpy of sublimation of M is ΔHsub = 111 kJ/mol. The first and second ionization energies of M are IE1 = 687 kJ/mol and IE2 = 1374 kJ/mol. The electron affinity of X is ΔHEA = –325 kJ/mol, and the bond energy of X2 is BE = 191 kJ/mol. I have researched various tutorials and followed the steps provided, but I am still unable to arrive at the correct answer.

Torey Skiles · Accepted Answer

Use Born-Haber(-Fajans) Cyclehttp://en.wikipedia.org/wiki/Born%E2%80%93Haber_cy...M(s)  +  X2(g)  &rarr; MX2(s)  &Delta;Hf&deg; = -759kJ mol^-1M(s) &rarr;&Delta;Hsub(M)&rarr;M(g) = 111 kJ mol^-1M(g) &rarr;&Delta;HIE1(M)&rarr; M^+  + e&#8315;  687 kJ mol^-1M^+&rarr;&Delta;HIE2(M)&rarr; M^2+ + e&#8315;  1374 kJ mol^-1 X2 &rarr;&Delta;HBE(X2)&rarr; 2X  191X + e&#8315;&rarr;&Delta;HEA1(X)&rarr;X^-  -141 kJ mol^-1&Delta;Hf&deg;  =  U  + &Delta;Hsub(M)  + IE1(M)  + IE2(M) +  &Delta;Hdiss(F2)  + 2&times; EA1(X) -759  = U  + 111 + 687 + 1374 + 191 &ndash; 2&times; 325U = -759 -111 -687 -1374 -191 + 650 = -2472 kJ mol^-1-ve sign usually dropped; should only be three sig figs

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determine lattice energy given this information?

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