Textbook Question
Indicate the principal type of solute–solvent interaction in each of the following solutions and rank the solutions from weakest to strongest solute–solvent interaction: (b) CH2Cl2 in benzene (C6H6)
Ch.13 - Properties of Solutions
Chapter 13, Problem 17b
An ionic compound has a very negative ∆Hsoln in water (b) Which term would you expect to be the largest negative number: ∆Hsolvent, ∆Hsolute, or ∆Hmix?
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Understand that the enthalpy of solution (∆H_{soln}) is the sum of three components: ∆H_{solute}, ∆H_{solvent}, and ∆H_{mix}.
Recognize that a very negative ∆H_{soln} indicates that the overall process of dissolving the ionic compound in water is highly exothermic.
Recall that ∆H_{solute} is the energy required to break the ionic bonds in the solute, which is typically positive.
Recall that ∆H_{solvent} is the energy required to disrupt the intermolecular forces in the solvent, which is also typically positive.
Conclude that ∆H_{mix}, which is the energy released when new interactions form between the solute and solvent, must be the largest negative number to result in a very negative ∆H_{soln}.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
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 very negative ∆H<sub>soln</sub> indicates that the dissolution process is exothermic, meaning it releases heat. This is often the case for ionic compounds, where the energy released from solute-solvent interactions exceeds the energy required to separate the solute particles.
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Enthalpy of Formation
Enthalpy Changes in Solution Process
The dissolution of a solute in a solvent involves three key enthalpy changes: ∆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). Understanding these components helps in predicting the overall enthalpy change during the dissolution process and determining which term will be the largest negative value.
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Comparison of Enthalpy Terms
In the context of an ionic compound dissolving in water, the term ∆H<sub>mix</sub> is typically the largest negative number because it represents the strong interactions formed between the ions and water molecules. This strong solvation energy often outweighs the energy required to separate both the solute and solvent, leading to a significant release of energy during the mixing process.
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Related Practice
Textbook Question
Indicate the principal type of solute–solvent interaction in each of the following solutions and rank the solutions from weakest to strongest solute–solvent interaction: (c) methanol (CH3OH) in water
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Textbook Question
When ammonium chloride dissolves in water, the solution becomes colder. (a) Is the solution process exothermic or endothermic?
Textbook Question
When ammonium chloride dissolves in water, the solution becomes colder. (b) Why does the solution form?
Textbook Question
The first stage of treatment at the reverse osmosis plant in Carlsbad, California, is to flow the water through rock, sand, and gravel as shown here. Would this step remove particulate matter? Would this step remove dissolved salts?
[Section 18.4]