How does increasing carbon chain length affect the boiling point of alkanes, and why?

How does increasing carbon chain length affect the boiling point of alkanes, and why?

• A. It remains constant due to similar molecular weights.
• B. It increases due to stronger London dispersion forces.
• C. It decreases due to weaker dipole interactions.
• D. It increases due to hydrogen bonding.

Answer: (B)

Increasing chain length in alkanes raises the boiling point because the main intermolecular force is London dispersion (van der Waals) forces, which get stronger as the molecule becomes larger. Longer chains have more electrons and a bigger surface area, allowing larger temporary dipoles and thus stronger dispersion forces between molecules. With stronger forces, more energy is needed to separate the molecules into a gas, so the boiling point increases. Alkanes are nonpolar, so there are no dipole-dipole interactions or hydrogen bonding to drive a different trend. The idea that the boiling point stays constant is not correct, since bigger molecules experience stronger dispersion forces.

Increasing chain length in alkanes raises the boiling point because the main intermolecular force is London dispersion (van der Waals) forces, which get stronger as the molecule becomes larger. Longer chains have more electrons and a bigger surface area, allowing larger temporary dipoles and thus stronger dispersion forces between molecules. With stronger forces, more energy is needed to separate the molecules into a gas, so the boiling point increases. Alkanes are nonpolar, so there are no dipole-dipole interactions or hydrogen bonding to drive a different trend. The idea that the boiling point stays constant is not correct, since bigger molecules experience stronger dispersion forces.