What happens to the entropy (∆S) during the formation of a solution?

When a solute dissolves in a solvent to form a solution, the overall disorder of the system generally increases, which corresponds to an increase in entropy (∆S). This increase in entropy occurs because the solute particles become dispersed within the solvent, leading to a greater number of possible positions and orientations for the solute and solvent molecules compared to when they are in their pure states.

In more detail, when a solid solute is added to a liquid solvent, the structured lattice of the solid breaks apart as the solute molecules interact with the solvent. This disruption of the solid structure and the resultant mixing with the solvent contributes to a more disordered arrangement of molecules. The greater the randomness in the arrangement of molecules, the higher the entropy.

In some cases, the increase in entropy can be driven by large amounts of solute being added and can also be influenced by how the solute interacts with the solvent. However, generally speaking, mixing tends to result in an increase in entropy regardless of the solute involved, which holds true for most situations in solution formation.

Therefore, the correct answer is that entropy increases during the formation of a solution, reflecting the greater disorder in the system as the solute and solvent mix.