Chapter 23, Problem 60A

Interpretation Introduction

Interpretation: To explain the reason for the difference in the boiling point of propane and acetaldehyde having the same molar masses.

Concept Introduction: Several factors affect the boiling point apart from the molar masses. The boiling point is affected by the pressure, impurities present, intermolecular forces, and branching.

Answer to Problem 60A

Propane has only van der Waal forces of attraction whereas, acetaldehyde has dipole-dipole interactions. Therefore, acetaldehyde has a higher boiling point as compared to that of propane.

Explanation of Solution

In the case of propane, there are van der Waals forces of attraction present. These forces are weak forces that account for the low boiling point of propane. Whereas, in the case of acetaldehyde dipole-dipole interactions are present due to the presence of the carbonyl group which is stronger than the Vander Waals forces of attraction that account for the higher boiling point of acetaldehyde. Therefore, acetaldehyde has a higher boiling point as compared to than of propane.

Conclusion

Intermolecular forces present in the molecule will affect the boiling point of the molecule. If intermolecular forces are weak then the boiling point will be low because less energy is required to break the bonds. If intermolecular forces are strong then the boiling point will be high because high energy is required to break the bond.