Concept:Lattice energy can be defined from two opposing perspectives: the energy required to break apart an ionic lattice, or the energy released when forming it. Standard IUPAC definitions often align it with a specific type of formation.
Formula:$$ X^+_{(g)} + Y^-_{(g)} \rightarrow XY_{(s)} \quad \Delta H = -ve \text{ (Lattice Formation)} $$
Solution:- By convention, Lattice Energy is often defined as the enthalpy change when one mole of an ionic solid is formed from its constituent gaseous ions.
- Because gas-phase ions are coming together to form a highly stable, tightly packed solid matrix, a tremendous amount of energy is released.
- Therefore, in this context, it represents the enthalpy of Formation of the lattice.
Why other options are incorrect:Combustion involves reaction with oxygen. Dissolution is dissolving in a solvent. While dissociation is the reverse of lattice formation (breaking the lattice apart), the test context explicitly maps lattice energy conceptually to the structural formation step in Born-Haber cycles.
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