Chemistry 122:Energetics of Solution Formation

Chemistry 122:Energetics of Solution Formation - Chemistry...

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Chemistry 122 1/27/2014 Energetics of Solution Formation The solution process is accompanied by changes in enthalpy. Example: when NaCl dissolves in H 2 O, the process is slightly endothermic ΔH sol = 3.9 kJ/mol. Three processes affect the energetics of solution: 1. Separation of solute particles ( ΔH solute ) 2. Separation of solvent particles ( ΔH solvent ), 3. New interactions between solute and solvent ( ΔH mix ). The enthalpy change of the overall process depends on H for each of these steps. Recall Hess’s Law: ΔH sol = ΔH solute + ΔH solvent + ΔH mix The formation of a solution can be either exothermic or endothermic ( see next slide). *When you break in interaction, you need energy* The dropping of the kinetic energy means lower/less heat Just because a substance disappears when it comes in contact with a solvent, it doesn’t mean the substance dissolved. It may have reacted. Dissolution is a physical change—you can get back the original solute by evaporating the solvent.
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