Which of the following best describes the qualitative energy diagram for the dissolution of LiI in water?

• A. The energy diagram shows an initial increase in energy as LiI dissociates, followed by a larger decrease as ions are hydrated, resulting in an overall exothermic process.
• B. The energy diagram shows no change in energy, indicating the dissolution is neither exothermic nor endothermic.
• C. The energy diagram shows a decrease in energy as LiI dissociates, followed by a smaller increase as ions are hydrated, resulting in an overall endothermic process.
• D. The energy diagram shows a continuous increase in energy throughout the dissolution, indicating an endothermic process.

Answer: (A)

Verified step by step guidance

1. Understand that the dissolution of an ionic compound like LiI in water involves two main energy changes: the energy required to break the ionic lattice (lattice energy) and the energy released when ions are hydrated by water molecules (hydration energy).
2. Recognize that breaking the ionic lattice requires energy input, so this step corresponds to an increase in the system's energy (endothermic step).
3. Next, when the separated Li⁺ and I⁻ ions interact with water molecules, hydration occurs, releasing energy and causing a decrease in the system's energy (exothermic step).
4. Compare the magnitudes of these energy changes: if the hydration energy released is greater than the lattice energy absorbed, the overall process is exothermic, resulting in a net decrease in energy after the initial increase.
5. Therefore, the qualitative energy diagram should show an initial rise in energy as the lattice breaks, followed by a larger drop as ions are hydrated, indicating an overall exothermic dissolution process.