Understanding the Higher Boiling Point of CHBr3 Compared to CHBr2: Factors Influencing Vaporization

When considering the boiling points of chemical compounds, several factors come into play, including molecular weight, intermolecular forces, and molecular structure. In this article, we will explore these factors to explain why CHBr3 (bromoform) has a higher boiling point compared to CHBr2 (dibromomethane).

Key Factors Influencing Boiling Point

The boiling point of a compound is a critical physical property, influenced by several factors:

Molecular Weight

The boiling point of a compound is generally directly related to its molecular weight. A higher molecular weight typically results in stronger London dispersion forces, a type of van der Waals force that significantly contributes to a higher boiling point. In the case of CHBr3 (bromoform) and CHBr2 (dibromomethane), the differences in their molecular weights are noteworthy.

CHBr3 has a molecular weight of approximately 252 g/mol, whereas CHBr2 has a molecular weight of about 173 g/mol.

Given that CHBr3 has a higher molecular weight, it exhibits stronger London dispersion forces, contributing to its higher boiling point.

Intermolecular Forces

Both CHBr3 and CHBr2 exhibit dipole-dipole interactions due to the polar C-Br bonds. However, the larger size and mass of CHBr3 enhance these interactions compared to CHBr2, leading to a higher boiling point.

The strength of these intermolecular forces is further amplified by the additional presence of Bromine (Br) atoms in CHBr3. The large electron cloud and extra electrons contribute to more significant London dispersion forces.

Molecular Structure

Examining the molecular structures, we can see that CHBr3 is a tetrahedral molecule with three bromine atoms, while CHBr2 has two hydrogen atoms and two bromine atoms. The presence of more bromine atoms in CHBr3 leads to stronger overall intermolecular attractions.

Conclusion

The combination of higher molecular weight, stronger London dispersion forces, and more significant dipole-dipole interactions in CHBr3 results in a higher boiling point compared to CHBr2.

Comparison of Boiling Points

According to experimental data, the normal boiling points are as follows:

Bromoform (CHBr3): 149.1 °C Dibromomethane (CHBr2): 97.0 °C Tetrabromomethane (CBr4): 94.5 °C

Bromoform (CHBr3) has a higher boiling point due to its additional bromine atoms and larger molecular weight, leading to stronger intermolecular forces. In contrast, dibromomethane (CHBr2) has a lower boiling point because of its lower molecular weight and weaker intermolecular forces.