Final answer:
Energy is absorbed to break intermolecular forces during dissolution, and whether the process is endothermic or exothermic depends on the balance of energy absorbed and released.
Step-by-step explanation:
The dissolution process involves energy changes related to intermolecular forces. These forces include solute-solute, solvent-solvent, and solute-solvent attractions. To dissolve a solid, energy must be absorbed to overcome the solute-solute and solvent-solvent attractions, which are endothermic processes. Conversely, when solute-solvent attractions are established during solvation, energy is released, an exothermic process. The balance between the energy absorbed in breaking up these forces and the energy released during solvation determines if the overall dissolution process is endothermic or exothermic.
In some cases, if the energy required to separate the solute and solvent is much greater than the energy released during solvation, the substances will not form a solution. Moreover, the breaking of intermolecular forces in a phase change from solid to liquid or liquid to vapor requires significant energy, as depicted in Figure 14.7. No temperature change occurs until a phase change is complete, indicating that all energy input goes into changing the phase by overcoming molecular attractions rather than increasing thermal energy.