How does increasing the molecular weight of alkanes generally affect their boiling points?

How does increasing the molecular weight of alkanes generally affect their boiling points?

• A. It decreases their boiling points
• B. It has no effect on their boiling points
• C. It raises their boiling points
• D. It creates an unstable compound

Answer: (C)

Increasing the molecular weight of alkanes generally raises their boiling points due to enhanced van der Waals forces (also known as London dispersion forces) between the molecules. As the molecular weight increases, the number of electrons in the molecule also increases, which leads to a greater polarizability. This means that larger alkane molecules can form temporary dipoles more effectively, resulting in stronger intermolecular attractions. As a result, more energy (in the form of heat) is required to overcome these intermolecular forces during the phase transition from liquid to gas, leading to an increase in boiling point. This trend is observed with a series of alkanes where the boiling points get progressively higher as the carbon chain length increases. For example, as you go from methane (the simplest alkane) to longer-chain alkanes like pentane or hexane, the boiling point increases due to this effect. The relationship between molecular weight and boiling point is significant in organic chemistry, particularly when analyzing the physical properties of different alkanes and predicting their behavior in various chemical contexts.

Increasing the molecular weight of alkanes generally raises their boiling points due to enhanced van der Waals forces (also known as London dispersion forces) between the molecules. As the molecular weight increases, the number of electrons in the molecule also increases, which leads to a greater polarizability. This means that larger alkane molecules can form temporary dipoles more effectively, resulting in stronger intermolecular attractions.

As a result, more energy (in the form of heat) is required to overcome these intermolecular forces during the phase transition from liquid to gas, leading to an increase in boiling point. This trend is observed with a series of alkanes where the boiling points get progressively higher as the carbon chain length increases. For example, as you go from methane (the simplest alkane) to longer-chain alkanes like pentane or hexane, the boiling point increases due to this effect.

The relationship between molecular weight and boiling point is significant in organic chemistry, particularly when analyzing the physical properties of different alkanes and predicting their behavior in various chemical contexts.