Which of the following have a higher boiling point: HCl, HBr, H2O, or Br2?
The Correct Answer and Explanation is:
The correct answer is: H₂O has the highest boiling point among HCl, HBr, H₂O, and Br₂.
Explanation:
Boiling point is influenced by the type and strength of intermolecular forces present in a substance. The stronger these forces, the more energy (in the form of heat) is required to separate the molecules and turn the substance from liquid to gas, leading to a higher boiling point.
Let’s analyze the intermolecular forces of each compound:
1. H₂O (Water)
Water molecules form strong hydrogen bonds, which are the most powerful type of dipole-dipole interaction. Hydrogen bonding occurs in molecules where hydrogen is bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine. In water, the oxygen atom attracts the hydrogen atoms of neighboring water molecules, creating a strong network of hydrogen bonds. These interactions significantly raise the boiling point of water, which is 100°C at standard pressure.
2. HCl (Hydrogen Chloride)
HCl has dipole-dipole interactions due to the difference in electronegativity between hydrogen and chlorine. However, HCl does not exhibit hydrogen bonding because chlorine is not electronegative enough, nor does it have a small enough atomic radius to facilitate hydrogen bonding. Its boiling point is much lower than water, around –85°C.
3. HBr (Hydrogen Bromide)
HBr is similar to HCl in structure but has a larger molar mass and slightly stronger London dispersion forces. Its boiling point is around –67°C, higher than HCl but still much lower than water.
4. Br₂ (Bromine)
Br₂ is a nonpolar molecule, so it only exhibits London dispersion forces. These are weaker than hydrogen bonds but can be stronger than dipole-dipole forces if the molecule is large. Br₂ has a boiling point of 59°C, which is relatively high for a nonpolar molecule but still lower than water.
Conclusion:
Among the four, water (H₂O) has the highest boiling point due to its strong hydrogen bonding.
