Carbon tetrachloride, CCl4, has a higher boiling point than methane, CH4, because… a the dipole-dipole forces in carbon tetrachloride are stronger than they are in methane b the dipole-dipole forces in carbon tetrachloride are weaker than they are in methane c the London dispersion forces in carbon tetrachloride are stronger than they are in methane d the London dispersion forces in carbon tetrachloride are weaker than they are in methane e the C-Cl bond is stronger than the C-H bond
The Correct Answer and Explanation is:
The correct answer is c: the London dispersion forces in carbon tetrachloride are stronger than they are in methane.
Here’s the explanation:
The boiling point of a substance is influenced by the strength of the intermolecular forces between its molecules. These forces need to be overcome for the substance to transition from a liquid to a gas.
- Carbon Tetrachloride (CCl4) is a nonpolar molecule, meaning it doesn’t have a permanent dipole. However, it has a larger number of electrons (due to the size of the carbon and chlorine atoms), which increases its London dispersion forces. These forces arise from temporary fluctuations in electron distribution, creating temporary dipoles that induce dipoles in neighboring molecules. Larger molecules with more electrons tend to have stronger dispersion forces, and carbon tetrachloride is a relatively large molecule with a high molecular weight, leading to stronger London dispersion forces.
- Methane (CH4), on the other hand, is also a nonpolar molecule but is much smaller than carbon tetrachloride. It has fewer electrons, and as a result, its London dispersion forces are weaker. The small size of methane means its molecules are held together by relatively weak intermolecular forces compared to carbon tetrachloride.
Because the London dispersion forces in carbon tetrachloride are stronger, more energy is required to overcome these forces during the phase transition from liquid to gas, resulting in a higher boiling point for carbon tetrachloride compared to methane.
Other options can be ruled out:
- a: Carbon tetrachloride is nonpolar, so there are no dipole-dipole forces in either molecule.
- b: The dipole-dipole forces are irrelevant here because both molecules are nonpolar.
- d: The London dispersion forces in CCl4 are stronger, not weaker, than those in CH4.
- e: The strength of the C-H bond and C-Cl bond doesn’t directly affect the boiling point of the substance; it’s the intermolecular forces that matter here
