Two nonpolar organic liquids, hexane (C 6 H 14 ) and heptane (C 7 H 16 ), are mixed. (a) Do you expect ∆H soln to be a large positive number, a large negative number, or close to zero? Explain.

hi everyone for this problem. It reads to organic liquids with a very similar London dispersion force are mixed. What is the expected change in entropy of solution of the mixture explain. Okay, so we're looking for the expected change in entropy of the solution. So let's recall the change in entropy of our solution is going to equal the sum of the change in entropy of our salute plus the change in entropy of our solvent plus the change in entropy of our mixture. Okay. Since both of the liquids have a very similar London dispersion force, which is what we're told here. They have a very similar London dispersion force. The energy required to separate them individually and the energy released when they are mixed are approximately equal. Okay. And so what this means is our change in entropy of the solute plus the change in entropy of our solvent is going to equal. A negative change in entropy of our mixture. And what this translates to is our change in entropy of the solution is nearly zero. Okay. And so the correct answer choice here is going to be a and that reads the expected change in entropy of the solution will be close to zero because the change in entropy of the solute and solvent will be almost equal. Okay, so a is our correct answer here. And that is the explanation. That's the end of this problem. I hope this was helpful

Ch.13 - Properties of Solutions

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Brown 14th Edition

Ch.13 - Properties of Solutions

Problem 21a

Chapter 13, Problem 21a

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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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. 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.

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Two nonpolar organic liquids, hexane (C₆H₁₄) and heptane (C₇H₁₆), are mixed. (b) Hexane and heptane are miscible with each other in all proportions. In making a solution of them, is the entropy of the system increased, decreased, or close to zero, compared to the separate pure liquids?

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KBr is relatively soluble in water, yet its enthalpy of solution is + 19.8 kJ/mol. Which of the following statements provides the best explanation for this behavior? (a) Potassium salts are always soluble in water. (b) The entropy of mixing must be unfavorable. (c) The enthalpy of mixing must be small compared to the enthalpies for breaking up water–water interactions and K–Br ionic interactions. (d) KBr has a high molar mass compared to other salts like NaCl.

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.

Verified video answer for a similar problem:

Key Concepts

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

Intermolecular Forces

Like Dissolves Like Principle

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.