Final answer:
When the heat of solution is large and exothermic, the energy released from hydrating the ions is greater than the energy it costs to separate the ions.
Step-by-step explanation:
When the heat of solution is large and exothermic, it means that a significant amount of energy is released when the ions in the solid compound are hydrated. The energy released from hydrating the ions is greater than the energy it costs to separate the ions.
This is because the formation of ionic compounds is usually extremely exothermic, and the strength of the electrostatic attraction between ions with opposite charges is directly proportional to the magnitude of the charges on the ions.