Lattice energy is considered exothermic. This energy is released when gaseous ions combine to form an ionic solid. The formation of a solid from its gaseous ions is a significant process in the stability of ionic compounds.
To explain further, when ions come together to form a crystal lattice, they release energy in the form of lattice energy. This release of energy is what makes the process exothermic. The stronger the attraction between the oppositely charged ions, the more energy is released during the formation of the lattice, leading to a more stable ionic compound.
In contrast, if energy is required to break apart the ionic solid into its gaseous ions, that process is endothermic. Thus, while the formation of the lattice releases energy (exothermic), breaking it apart requires energy (endothermic). However, when discussing lattice energy specifically in terms of its release during ionic bond formation, we categorize it as an exothermic process.