Question

The boiling point of carbon tetrachloride (CCl4) is higher than that of chloroform (CHCl3). Since chloroform is

polar and carbon tetrachloride is not, consideration of dipole-dipole forces would predict that chloroform would have the higher boiling point. How can we account for the observed order of the boiling points?

Answer 1

Despite CCl4 being nonpolar and CHCl3 polar, CCl4 has a higher boiling point due to its larger molar mass which leads to stronger London dispersion forces that trump the dipole-dipole interactions in CHCl3.

Step-by-step explanation:

The question reflects an observation that carbon tetrachloride (CCl4) has a higher boiling point than chloroform (CHCl3), even though CCl4 is nonpolar and CHCl3 is polar. Normally, one would expect polar molecules, which exhibit strong dipole-dipole interactions, to have higher boiling points than nonpolar molecules that rely on weaker London dispersion forces. However, in this case, CCl4 has a larger molar mass and a greater number of electrons than CHCl3, leading to stronger dispersion forces that outweigh the dipole-dipole interactions in CHCl3, resulting in a higher boiling point for CCl4. Thus, the strength of dispersion forces, which increase with the size and molar mass of the molecule, can sometimes overcome the effects of polarity on boiling points.