Chloroform (CHCl₃) and methane (CH₄) have different boiling points primarily due to differences in molecular interactions attributable to their respective molecular compositions and the presence of polar bonds.
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Molecular Composition: Chloroform contains chlorine atoms, which are much more electronegative than the hydrogen atoms in methane. This difference in electronegativity creates a significant dipole moment in chloroform, making it a polar molecule. In contrast, methane is a nonpolar molecule due to its symmetrical tetrahedral shape and the similar electronegativities of carbon and hydrogen.
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Intermolecular Forces: The presence of polar bonds in chloroform leads to dipole-dipole interactions between chloroform molecules. These interactions are stronger than the van der Waals (dispersion) forces present in methane, which is nonpolar. Consequently, more energy (in the form of heat) is required to break these dipole-dipole interactions in chloroform compared to the relatively weaker van der Waals forces in methane.
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Boiling Points: As a result of the stronger intermolecular forces in chloroform, it has a boiling point of about 61.2 °C, while methane, with weaker van der Waals forces, has a boiling point of about -161.5 °C. This difference in the boiling points is a direct consequence of the types of intermolecular forces operating in each substance.
In summary, although chloroform and methane may share some similarities in molecular shape, their differing properties—electronegativity of constituent atoms, polarity, and types of intermolecular forces—lead to the significant difference in their boiling points.
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