Final answer:
Calcium oxide (CaO) requires the most energy to convert one mole of the solid into separate ions due to its high-charged ions (Ca²⁺ and O²⁻) and the smaller ionic radii, leading to higher lattice energy compared to the other given compounds. The correct option is (e).
Step-by-step explanation:
The question asks which of the following compounds requires the most energy to convert one mole of the solid into separate ions: (a) K₂S, (b) K₂O, (c) CaS, (d) Cs₂S, or (e) CaO. T
his requires an understanding of lattice energy, which is the energy needed to separate one mole of a solid ionic compound into its gaseous ions. Lattice energy depends on the charge of the ions and the ionic radii; compounds with higher charged ions and smaller radii generally have higher lattice energies.
Reviewing the choices, CaO stands out because it contains Ca²⁺ and O²⁻ ions, indicating it would have a high lattice energy due to the double charges on both ions.
Furthermore, since Ca²⁺ is a smaller ion than K⁺ or Cs⁺, and O²⁻ is smaller than S²⁻, CaO has smaller ionic radii compared to other choices, suggesting tighter packing and higher lattice energy. Hence, CaO should require the most energy to separate into ions. Option (e) is the correct one.