Which statement best explains why water has a higher boiling point than ethane?

• A. Ethane molecules have stronger dipole-dipole interactions than water.
• B. Water molecules form strong hydrogen bonds, which require more energy to break during boiling.
• C. Water molecules are nonpolar, resulting in weaker intermolecular forces.
• D. Water has a larger molar mass than ethane, leading to stronger London dispersion forces.

Answer: (B)

Verified step by step guidance

1. Identify the types of intermolecular forces present in water and ethane. Water molecules exhibit hydrogen bonding due to the presence of highly electronegative oxygen atoms bonded to hydrogen, while ethane molecules primarily experience London dispersion forces because they are nonpolar.
2. Understand that hydrogen bonds are a special, strong type of dipole-dipole interaction that occur when hydrogen is bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine. These bonds require more energy to break compared to other intermolecular forces.
3. Recognize that boiling point is directly related to the strength of intermolecular forces: stronger forces require more energy (higher temperature) to overcome during the phase change from liquid to gas.
4. Compare the molecular polarity and molar masses: water is polar and forms hydrogen bonds, whereas ethane is nonpolar with weaker London dispersion forces. Although molar mass can influence boiling point, the difference in intermolecular forces is more significant here.
5. Conclude that water's higher boiling point is best explained by the presence of strong hydrogen bonds between its molecules, which require more energy to break compared to the weaker forces in ethane.