The lower it is, the more exothermic the reaction will be. As in part (b), the bond energy is a positive energy.This would make the reaction more exothermic, as a smaller positive value is “more exothermic.” A lower ionization energy is a lower positive energy in the Born-Haber cycle.Since the lattice energy is negative in the Born-Haber cycle, this would lead to a more exothermic reaction. The smaller the radius of the cation, the shorter the interionic distance and the greater the lattice energy would be.Recall that the more negative the overall value, the more exothermic the reaction is. In each case, think about how it would affect the Born-Haber cycle. The answer is (d), which requires about 740 kJ/mol.ģ. U may be calculated from the Born-Haber cycle. The lattice energy, U, is the energy required to convert the solid into separate ions. We begin with the elements in their most common states, Cs( s) and F 2( g). The Born-Haber cycle shows the relative energies of each step involved in the formation of an ionic solid from the necessary elements in their reference states.
