The standard heat of formation of nabr is -360.0 kj mol-1. the energy needed to vaporize one mole of br2(l) to give br2(g) is 31 kj mol-1. energy needed to vaporize one mole of na(s) is 107.8 kj. the first ionization energy of na is 495.4 kj mol-1. the bond energy of br2 is 192 kj per mole of br—br bonds. the lattice energy of nabr is -743.3 kj mol-1.