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Chapter 11: Problem 21

When pure methanol is mixed with water, the resulting solution feels warm. Would you expect this solution to be ideal? Explain.

Short Answer

Expert verified
The methanol-water solution cannot be considered ideal because there is a release of heat when the components are mixed, indicating a negative enthalpy change (ΔH_mix < 0). This suggests differences in molecular interactions within the solution compared to those in the pure components before mixing, which does not meet the criteria for an ideal solution.

Step by step solution

01

Understanding Ideal Solutions

An ideal solution is a mixture of two substances that follows Raoult's Law, which states that the vapor pressure of each component in the mixture is directly proportional to its mole fraction. In an ideal solution, the interactions between the molecules of the components in the solution are approximately the same as the interactions between the molecules of the individual components before mixing. This means that an ideal solution must not have any significant changes in enthalpy (the internal energy of the system) upon mixing.
02

Enthalpy Change and Ideal Solutions

In order for a solution to be considered ideal, the change in enthalpy (ΔH_mix) upon mixing should be approximately zero. This means that there is no heat absorbed or released during the mixing process. If there is a significant release or absorption of heat when two components are mixed together, it indicates that the interactions between the molecules of the components in the solution are different from the interactions between the individual components before mixing. As a result, the solution will not be ideal.
03

Methanol-Water Solution Feels Warm

The given information in the exercise states that when pure methanol is mixed with water, the resulting solution feels warm. This warmth indicates that heat has been released during the mixing process, which implies a negative enthalpy change (ΔH_mix < 0). The release of heat suggests that there are differences in the molecular interactions between methanol and water before and after mixing.
04

Conclusion

Based on the information given and our analysis above, we can conclude that the methanol-water solution cannot be considered an ideal solution. This is because there is a release of heat when the methanol and water are mixed together, indicating a negative enthalpy change (ΔH_mix < 0) and suggesting that the molecular interactions in the solution are different than those in the pure components before mixing.

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Most popular questions from this chapter

An unknown compound contains only carbon, hydrogen, and oxygen. Combustion analysis of the compound gives mass percents of \(31.57 \% \mathrm{C}\) and \(5.30 \% \mathrm{H}\). The molar mass is determined by measuring the freezing- point depression of an aqueous solution. A freezing point of \(-5.20^{\circ} \mathrm{C}\) is recorded for a solution made by dissolving \(10.56 \mathrm{~g}\) of the compound in \(25.0 \mathrm{~g}\) water. Determine the empirical formula, molar mass, and molecular formula of the compound. Assume that the compound is a nonelectrolyte.

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