Ionization energy of Cl– is 349 KJ/mole. Approximate heat liberated when an electron is added to gaseous chlorine atom.

Given Cl-(g) →Cl(g)+e- ΔH = +349 KJCl(g) + e- → Cl- (g) ΔH = -349 KJ6.023x1023 atoms of Cl(g) →Cl-(g) releases 349 KjOne atom of Cl(g)→Cl- releases  =                                               = 59x10-23 KJ                                               = 59x10-20 J                                               = 5.9x10-19 J