Recall the two conceptual steps necessary to dissolve a solute and form a solution
Key Points
There are two conceptual steps to form a solution, each corresponding to one of the two opposing forces that dictate solubility.
The first conceptual step is dissolution, which corresponds to the force of the solvent-solvent and solute-solute intermolecular attractions that needs to be broken down.
The second conceptual step is solvation, which corresponds to the force of the solute-solvent intermolecular attraction that needs to be formed in order to form a solution.
Many intermolecular forces can contribute to solvation, including hydrogen bonding, dipole-dipole forces, Van Der Waals forces, and ion-dipole interactions.
Term
intermolecular forcesattractive and repulsive forces between molecules
The strength of the intermolecular forces between solutes and solvents determines the solubility of a given solute in a given solvent. In order to form a solution, the solute must be surrounded, or solvated, by the solvent. Solutes successfully dissolve into solvents when solute-solvent bonds are stronger than either solute-solute bonds or solvent-solvent bonds.
Qualitatively, one can determine the solubility of a solute in a solvent by using the rule “like dissolves like”. In general, solutes whose polarity matches that of the solvent will generally be soluble. For example, table salt (NaCl) dissolves easily into water (H2O) because both molecules are polar.
Intermolecular Forces and Their Importance in Solution Formation
There are two conceptual steps to form a solution, each corresponding to one of the two opposing forces that dictate solubility. If the solute is a solid or liquid, it must first be dispersed — that is, its molecular units must be pulled apart. This requires energy, and so this step always works against solution formation (always endothermic, or requires that energy be put into the system).
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