Which property increases as the molecular size of alcohols increases?

Which property increases as the molecular size of alcohols increases?

• A. Solubility in water
• B. Flammability
• C. Melting and boiling points
• D. Reactivity with acids

Answer: (C)

As the molecular size of alcohols increases, the melting and boiling points also increase. This occurs because larger alcohol molecules have longer carbon chains, leading to a greater surface area that enhances van der Waals (dispersion) forces between the molecules. As these intermolecular forces become stronger with increasing chain length, more energy is required to separate the molecules during phase changes, resulting in higher melting and boiling points. In smaller alcohols, such as methanol and ethanol, hydrogen bonding contributes significantly to their physical properties, including lower boiling points. However, as the size of the alcohol increases, while hydrogen bonding may still play a role, the increased van der Waals forces become more dominant, causing the overall increase in boiling and melting points compared to the smaller alcohols.

As the molecular size of alcohols increases, the melting and boiling points also increase. This occurs because larger alcohol molecules have longer carbon chains, leading to a greater surface area that enhances van der Waals (dispersion) forces between the molecules. As these intermolecular forces become stronger with increasing chain length, more energy is required to separate the molecules during phase changes, resulting in higher melting and boiling points.

In smaller alcohols, such as methanol and ethanol, hydrogen bonding contributes significantly to their physical properties, including lower boiling points. However, as the size of the alcohol increases, while hydrogen bonding may still play a role, the increased van der Waals forces become more dominant, causing the overall increase in boiling and melting points compared to the smaller alcohols.