A molecule of CHCl3 (chloroform), has the same shape as a molecule of carbon tetrahydride, CH4. But carbon tetrahydride’s boiling point is -164º C and chloroform’s boiling point is 62 ºC. Explain the difference between the boiling points of the two substances.
please help !! so stressed :)
When I was in school the explanation was that the molar mass of CCl4 was so much higher and boiling points generally increas with increasing molar mass. I think the modern answer is intermolecular forces. In this case the dispersion forces for CCl4 are higher for CCl4 than for CH4 (more electrons in CCl4).
The difference in boiling points between chloroform (CHCl3) and carbon tetrahydride (CH4) can be explained by examining the intermolecular forces in each compound.
In carbon tetrahydride (CH4), there are only weak dispersion forces between the molecules. These forces arise due to temporary shifts in electron density, creating temporary partial charges that attract neighboring molecules. These dispersion forces are relatively weak, resulting in a low boiling point of -164 ºC.
On the other hand, in chloroform (CHCl3), in addition to dispersion forces, there are also significant dipole-dipole interactions. These dipole-dipole interactions arise due to the difference in electronegativity between carbon and chlorine atoms. Chlorine being more electronegative than carbon creates a partial negative charge on the chlorine atom and a partial positive charge on the carbon atom. This creates a dipole moment within each molecule, and these dipoles can attract each other. In addition, chloroform can also form hydrogen bonds due to the presence of the Cl-H bond, which results in stronger intermolecular forces compared to CH4. These stronger dipole-dipole interactions and hydrogen bonding lead to a higher boiling point of 62 ºC for chloroform.
In summary, the difference in boiling points between chloroform and carbon tetrahydride can be attributed to the stronger intermolecular forces (dipole-dipole interactions and hydrogen bonding) present in chloroform compared to the weak dispersion forces in carbon tetrahydride.