Which of the following reactions is associated with the lattice energy (ΔH_{latt}) of Li_2O?

• A. Li_2O(s) → 2Li^+(g) + O^{2-}(g)
• B. 2Li(s) + rac{1}{2}O_2(g) → Li_2O(s)
• C. Li_2O(s) → 2Li^+(aq) + O^{2-}(aq)
• D. 2Li^+(g) + O^{2-}(g) → Li_2O(s)

Answer: (D)

Verified step by step guidance

1. Understand that lattice energy (ΔH_{latt}) is defined as the energy change when one mole of an ionic solid forms from its gaseous ions. It is usually considered as the energy released when gaseous ions combine to form the solid lattice.
2. Look at the given reactions and identify which one represents the formation of the solid ionic compound from its gaseous ions. The lattice energy corresponds to the reaction where gaseous ions come together to form the solid.
3. The reaction Li_2O(s) → 2Li^+(g) + O^{2-}(g) represents the decomposition of the solid into gaseous ions, which is the reverse of lattice energy and is called lattice dissociation energy.
4. The reaction 2Li(s) + \frac{1}{2}O_2(g) → Li_2O(s) represents the formation of the solid from elemental lithium and oxygen in their standard states, which relates to the enthalpy of formation, not lattice energy.
5. The reaction 2Li^+(g) + O^{2-}(g) → Li_2O(s) shows gaseous ions combining to form the solid lattice, which directly corresponds to the lattice energy (ΔH_{latt}).