The boiling point of a liquid is the temperature at which its vapor pressure equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid is affected by several factors, including the strength of the intermolecular forces between the molecules, the molecular weight of the liquid, and the surface area of the liquid.

Intermolecular forces

The strength of the intermolecular forces between the molecules in a liquid determines how much energy is required to overcome these forces and cause the liquid to boil. The stronger the intermolecular forces, the higher the boiling point of the liquid.

For example, water has a high boiling point (100°C) because of the strong hydrogen bonds between the water molecules. In contrast, methane has a low boiling point (-161.6°C) because the intermolecular forces between the methane molecules are weak.

Molecular weight

The molecular weight of a liquid also affects its boiling point. The heavier the molecules, the higher the boiling point of the liquid.

For example, octane has a higher boiling point (125.7°C) than heptane (98.4°C) because the octane molecules are heavier than the heptane molecules.

Surface area

The surface area of a liquid also affects its boiling point. The larger the surface area of the liquid, the lower the boiling point of the liquid.

For example, a small drop of water has a higher boiling point than a large pot of water because the small drop of water has a smaller surface area.

In general, the boiling point of a liquid increases with increasing molecular weight, increasing intermolecular forces, and decreasing surface area.