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.

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Understand the concept of \( \Delta H_{\text{soln}} \): It represents the enthalpy change when a solution is formed. For nonpolar substances, the interactions are primarily dispersion forces.

Consider the nature of hexane and heptane: Both are nonpolar organic liquids, meaning they have similar types of intermolecular forces (London dispersion forces).

When similar nonpolar substances mix, the energy required to break the intermolecular forces in the pure substances is similar to the energy released when new interactions are formed in the mixture.

Since the intermolecular forces in hexane and heptane are similar, the enthalpy change \( \Delta H_{\text{soln}} \) is expected to be close to zero, as there is little net energy change.

Conclude that \( \Delta H_{\text{soln}} \) is close to zero because the energy required to separate the molecules of each liquid is approximately equal to the energy released when they mix.

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주요 개념

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Enthalpy of Solution (∆H<sub>soln</sub>)

The enthalpy of solution (∆H<sub>soln</sub>) 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.

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