Two nonpolar organic liquids, hexane (C₆H₁₄) and heptane (C₇H₁₆), are mixed. (a) Do you expect ∆H_soln to be a large positive number, a large negative number, or close to zero? Explain.

Key Concepts

Enthalpy of Solution (∆H_soln)

The enthalpy of solution (∆H_soln) refers to the heat change that occurs when a solute dissolves in a solvent. It can be positive (endothermic), negative (exothermic), or close to zero, depending on the interactions between solute and solvent molecules. In the case of mixing two nonpolar liquids, the enthalpy change is often minimal due to similar intermolecular forces.

Intermolecular Forces

Intermolecular forces are the attractive forces between molecules that influence physical properties such as boiling point, melting point, and solubility. Nonpolar molecules like hexane and heptane primarily experience London dispersion forces, which are relatively weak. When two nonpolar substances are mixed, the similar types of intermolecular forces lead to minimal energy change.

Like Dissolves Like Principle

The 'like dissolves like' principle states that polar solvents dissolve polar solutes, and nonpolar solvents dissolve nonpolar solutes. Since both hexane and heptane are nonpolar, they are expected to mix well without significant energy changes. This principle helps predict that the enthalpy of solution for this mixture will be close to zero, as the interactions between the two liquids are similar.