Lattice energy is defined as what?

• A. The enthalpy change when 1 mole of an ionic compound is formed from its gaseous ions under standard conditions
• B. The energy required to break the lattice into gaseous ions
• C. The energy change when an ionic compound dissolves in water
• D. The energy change when a molten ionic compound forms gas

Answer: (A)

Lattice energy is the energy change when a solid ionic lattice is formed from gaseous ions. This is defined as the enthalpy change for forming 1 mole of an ionic compound from its gaseous ions under standard conditions, and it represents the energy released when the ions come together in the solid lattice (often shown as a negative value, with the magnitude being the lattice energy). This makes the formation definition the best descriptor for lattice energy. The energy to break the lattice into gaseous ions describes the reverse process and has the opposite sign. The other options refer to different processes (dissolving in water or converting a molten lattice to gas) and do not define lattice energy.