Why Do Different Liquids Have Different Boiling Points?

Different liquids have different boiling points because each liquid has a unique chemical makeup that gives it an identifying vapor pressure. When the vapor pressure of a liquid is equal to the pressure of the atmosphere, the liquid starts to boil.

One aspect that dictates the boiling point of a liquid is the amount of polarity between the molecules. Strong polar molecules have a higher boiling point than weak polar molecules. The strength of the bonds requires a higher amount of kinetic energy to break them apart. A higher amount of energy results in a higher vapor pressure.

Water is an example of a molecule with strong polar bonds. It boils at 212 degrees Fahrenheit because more energy is needed to break its bonds apart. Dimethyl ether is a molecule that has no polar bonds; it has a boiling point of approximately -11 degrees.

The vapor pressure of a liquid varies based on the surrounding environment. When a liquid is in a lower pressure environment, it has a lower boiling point. The same is true for liquids in a higher pressure environment: they have higher boiling points. This is because the vapor pressure has to be equivalent to the pressure of the atmosphere. When the atmospheric pressure is reduced, the vapor pressure is able to reach it more quickly.