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Ch.13 - Properties of Solutions
Brown - Chemistry: The Central Science 15th Edition
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Tutti i libri di testoBrown 15th EditionCh.13 - Properties of SolutionsProblema 20
Capitolo 13, Problema 20

For the dissolution of LiCl in water, ∆Hsoln = -37 kJ/mol. Which term would you expect to be the largest negative number: ∆Hsolvent, ∆Hsolute, or ∆Hmix?

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Understand the process of dissolution: When a solute dissolves in a solvent, three main enthalpy changes occur: ∆Hsolute (energy required to break apart the solute), ∆Hsolvent (energy required to separate the solvent molecules), and ∆Hmix (energy released when solute and solvent interact).
Recognize that ∆Hsoln is the overall enthalpy change for the dissolution process, given as -37 kJ/mol. This indicates that the process is exothermic, meaning it releases energy.
Consider the nature of each term: ∆Hsolute is typically positive because energy is required to break the solute into individual ions or molecules. ∆Hsolvent is also usually positive as energy is needed to disrupt the solvent structure.
Analyze ∆Hmix: This term is often negative because energy is released when the solute and solvent interact and form new bonds or attractions. Since the overall process is exothermic, ∆Hmix must be significantly negative to offset the positive values of ∆Hsolute and ∆Hsolvent.
Conclude that ∆Hmix is expected to be the largest negative number, as it must be sufficiently negative to result in the overall negative ∆Hsoln value of -37 kJ/mol.

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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. A negative value indicates that the process is exothermic, meaning heat is released into the surroundings. In this case, the dissolution of LiCl in water releases -37 kJ/mol, suggesting that the interactions between the solute and solvent are energetically favorable.
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Enthalpy of Formation

Enthalpy Changes in Dissolution

The dissolution process can be broken down into three components: ∆H<sub>solute</sub> (energy required to separate solute particles), ∆H<sub>solvent</sub> (energy required to separate solvent molecules), and ∆H<sub>mix</sub> (energy released when solute and solvent interact). The overall enthalpy change (∆H<sub>soln</sub>) is the sum of these three components, which helps in understanding the energetics of the dissolution process.
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Enthalpy of Formation

Thermodynamic Favorability

In thermodynamics, a process is considered favorable if it results in a decrease in enthalpy (exothermic) or an increase in entropy. For the dissolution of LiCl, the negative ∆H<sub>soln</sub> suggests that the process is thermodynamically favorable. The largest negative term among ∆H<sub>solvent</sub>, ∆H<sub>solute</sub>, or ∆H<sub>mix</sub> would likely be ∆H<sub>mix</sub>, as it represents the energy released when the solute and solvent interact, contributing significantly to the overall exothermic nature of the solution process.
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First Law of Thermodynamics
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