Which of the following best describes lattice dissociation enthalpy (lattice energy)?

• A. The energy released when one mole of gaseous ions forms an ionic solid.
• B. The energy required to break one mole of covalent bonds in a molecule.
• C. The energy change when one mole of a substance dissolves in water.
• D. The energy required to separate one mole of an ionic solid into its gaseous ions.

Answer: (D)

Verified step by step guidance

1. Understand that lattice dissociation enthalpy (also called lattice energy) refers to the energy change involved in breaking an ionic solid into its constituent gaseous ions.
2. Recall that lattice energy is defined as the energy required to separate one mole of an ionic solid into its gaseous ions, which means it is an endothermic process (energy is absorbed).
3. Recognize that the opposite process—formation of an ionic solid from gaseous ions—releases energy, so the lattice energy in that direction is negative (exothermic).
4. Distinguish lattice energy from other energy terms: bond dissociation enthalpy relates to covalent bonds, and enthalpy of solution relates to dissolving substances in water.
5. Conclude that the best description of lattice dissociation enthalpy is the energy required to separate one mole of an ionic solid into its gaseous ions.