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.
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The boiling points of substances are influenced by the intermolecular forces acting between their molecules. In the case of carbon tetrahydride (CH4) and chloroform (CHCl3), the difference in boiling points can be explained by the differences in their molecular structures and intermolecular forces.
First, let's look at the molecular structures of the two substances. A molecule of carbon tetrahydride (CH4) consists of a central carbon atom bonded to four hydrogen atoms, forming a tetrahedral shape. On the other hand, a molecule of chloroform (CHCl3) consists of a central carbon atom bonded to three hydrogen atoms and one chlorine atom, also forming a tetrahedral shape. So, both molecules have similar shapes.
Now, let's consider the intermolecular forces present in each substance. In carbon tetrahydride, the only intermolecular force present is London dispersion forces (also known as van der Waals forces), which arise from temporary fluctuations in electron density. These forces are relatively weak.
In contrast, chloroform molecules have dipole-dipole interactions, which arise due to the difference in electronegativity between chlorine and hydrogen atoms. Chlorine is more electronegative than hydrogen, creating a dipole moment in the molecule. Additionally, chloroform can also exhibit hydrogen bonding since the hydrogen atoms in chloroform are attached to electronegative atoms (chlorine) that can act as hydrogen bond acceptors.
Dipole-dipole interactions and hydrogen bonding are stronger intermolecular forces compared to London dispersion forces. These forces require more energy to overcome, meaning more heat is needed to break the intermolecular forces and convert the substance from a liquid to a gas.
Therefore, due to the presence of stronger intermolecular forces (dipole-dipole interactions and hydrogen bonding) in chloroform compared to carbon tetrahydride, chloroform has a higher boiling point. The higher boiling point of chloroform means that it requires more energy (higher temperature) to convert it from a liquid to a gas compared to carbon tetrahydride.
http://wiki.answers.com/Q/What_is_the_intramolecular_force_in_ccl4
Read about dispersion forces in your text or notes.