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Chapter 13: Problem 22

\(\mathrm{KBr}\) is relatively soluble in water, yet its enthalpy of solution is \(+19.8 \mathrm{~kJ} / \mathrm{mol}\). 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) \(\mathrm{KBr}\) has a high molar mass compared to other salts like \(\mathrm{NaCl}\)

Short Answer

Expert verified
Choice (c) The enthalpy of mixing must be small compared to the enthalpies for breaking up water-water interactions and K-Br ionic interactions.

Step by step solution

01

Answer Choice (a) Analysis

Potassium salts being always soluble in water doesn't explain how \(\mathrm{KBr}\) dissolves with positive enthalpy, so we can eliminate this choice.
02

Answer Choice (b) Analysis

The entropy of mixing refers to the increase in disorder when two substances mix. An unfavorable entropy of mixing would suggest that the dissolution process is less likely to occur, so this statement does not provide a good explanation.
03

Answer Choice (c) Analysis

This statement suggests that the enthalpy of mixing is small compared to the enthalpies required to break water-water and K-Br ion interactions. If this is true, then the overall enthalpy change could still be positive, but small enough for the dissolution to occur due to other factors (e.g. entropy change). This statement could provide a good explanation.
04

Answer Choice (d) Analysis

The high molar mass of \(\mathrm{KBr}\) compared to salts like \(\mathrm{NaCl}\) doesn't provide an explanation for its solubility in water with positive enthalpy of solution. This statement can be disregarded. From the analysis of each statement, it is clear that the best explanation for the given behavior of \(\mathrm{KBr}\) is provided by:
05

Final Answer

Choice (c) The enthalpy of mixing must be small compared to the enthalpies for breaking up water-water interactions and K-BR ionic interactions.

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