Calculate the lattice energy (U) of sodium oxide (Na2O) from the following data:

Ionization energy of Na(g) 495 kJ/mol

Electron affinity of O(g) for 2 e- 603 kJ/mol

Energy to vaporize Na(s) 109 kJ/mol

O2(g) bond energy 499 kJ/mol

Energy change for the reaction (2 Na (s) + 1/2 O2 (g)) -416 kJ/mol Na2O