What happens when the enthalpy change of a solution is negative in the context of vapor pressure?

When the enthalpy change of a solution is negative, it indicates that the process of dissolving a solute in a solvent is exothermic, meaning that heat is released during the dissolution. This release of energy can result in increased interactions between the solute and solvent molecules.

In terms of vapor pressure, a negative enthalpy change generally implies that the solution has stronger intermolecular forces than the pure solvent. As a result, the tendency for solvent molecules to escape into the vapor phase diminishes. This means that fewer molecules of the solvent can break free and enter the gas phase, leading to a reduction in the vapor pressure of the solution compared to the pure solvent.

Understanding this concept is crucial in predicting vapor pressure behavior in solutions. It illustrates how changes in enthalpy affect the physical properties of solutions, particularly how strong solute-solvent interactions can inhibit evaporation, thus lowering vapor pressure.