The Factors Affecting Boiling Point

Oct 13, 2025 by wbrum.org 9 views

In the world of organic chemistry, alkanes are a class of hydrocarbons that play a crucial role in various industrial and biological processes. These saturated hydrocarbons are characterized by their single bonds between carbon atoms, resulting in a stable and unreactive molecule. However, the physical properties of alkanes, such as their boiling points, can vary significantly depending on their molecular structure. In this article, we will explore the relationship between alkane structure and boiling point, and match the given alkanes in the order of increasing boiling point.

The Factors Affecting Boiling Point

Before we dive into the specifics of alkane boiling points, it's essential to understand the factors that influence this property. The boiling point of a substance is the temperature at which it changes state from a liquid to a gas. In the case of alkanes, the boiling point is primarily affected by the strength of the intermolecular forces between molecules. These forces can be categorized into three types: London dispersion forces, dipole-dipole interactions, and hydrogen bonding.

London Dispersion Forces: These are the weakest type of intermolecular force and arise due to temporary dipoles formed in nonpolar molecules. London dispersion forces increase with the size of the molecule, as larger molecules have more electrons and a greater chance of temporary dipoles forming.
Dipole-Dipole Interactions: These forces occur between polar molecules, where the positive end of one molecule is attracted to the negative end of another. Dipole-dipole interactions are stronger than London dispersion forces but weaker than hydrogen bonding.
Hydrogen Bonding: This is the strongest type of intermolecular force and occurs between molecules that have a hydrogen atom bonded to a highly electronegative atom, such as oxygen, nitrogen, or fluorine. Hydrogen bonding is responsible for the high boiling points of substances like water and ammonia.

Matching the Alkanes in Order of Increasing Boiling Point

Now that we have a basic understanding of the factors affecting boiling point, let's apply this knowledge to the given alkanes. We will match them in order of increasing boiling point based on their molecular structure and the strength of the intermolecular forces between molecules.

1. C2H6 (Ethane)

Ethane is the smallest molecule in the list, with a molecular weight of 30.07 g/mol. Due to its small size, ethane has the weakest London dispersion forces, resulting in the lowest boiling point among the given alkanes.

2. C9H20 (Nonane)

Nonane has a molecular weight of 128.23 g/mol, which is significantly larger than ethane. As a result, nonane has stronger London dispersion forces, leading to a higher boiling point than ethane.

3. C11H24 (Undecane)

Undecane has a molecular weight of 156.33 g/mol, making it larger than nonane. The increased size of undecane results in stronger London dispersion forces, leading to a higher boiling point than nonane.

4. C16H34 (Hexadecane)

Hexadecane has a molecular weight of 226.45 g/mol, which is larger than undecane. The increased size of hexadecane results in stronger London dispersion forces, leading to a higher boiling point than undecane.

5. C20H42 (Eicosane)

Eicosane has a molecular weight of 282.57 g/mol, making it larger than hexadecane. The increased size of eicosane results in stronger London dispersion forces, leading to a higher boiling point than hexadecane.

6. C32H66 (Tetratriacontane)

Tetratriacontane has a molecular weight of 442.81 g/mol, which is significantly larger than eicosane. The increased size of tetratriacontane results in stronger London dispersion forces, leading to a higher boiling point than eicosane.

7. C9H20 (Decane)

Decane has a molecular weight of 142.29 g/mol, which is larger than nonane. However, decane has a slightly lower boiling point than undecane due to its slightly smaller size.

Conclusion

In conclusion, the boiling point of an alkane is primarily affected by the strength of the intermolecular forces between molecules. The size of the molecule plays a crucial role in determining the strength of these forces, with larger molecules having stronger London dispersion forces. By understanding the relationship between alkane structure and boiling point, we can match the given alkanes in the order of increasing boiling point. The correct order is:

C2H6 (Ethane)
C9H20 (Nonane)
C9H20 (Decane)
C11H24 (Undecane)
C16H34 (Hexadecane)
C20H42 (Eicosane)
C32H66 (Tetratriacontane)

In our previous article, we explored the relationship between alkane structure and boiling point, and matched the given alkanes in the order of increasing boiling point. However, we understand that there may be many questions and doubts that readers may have regarding this topic. In this article, we will address some of the frequently asked questions and provide additional information to help clarify the concepts.

Q: What is the significance of alkane structure in determining boiling point?

A: The structure of an alkane plays a crucial role in determining its boiling point. The size of the molecule, the number of carbon atoms, and the arrangement of these atoms all contribute to the strength of the intermolecular forces between molecules. As a result, larger molecules with more carbon atoms tend to have higher boiling points.

Q: How do London dispersion forces affect the boiling point of an alkane?

A: London dispersion forces are the weakest type of intermolecular force and arise due to temporary dipoles formed in nonpolar molecules. These forces increase with the size of the molecule, as larger molecules have more electrons and a greater chance of temporary dipoles forming. As a result, larger alkanes tend to have higher boiling points due to stronger London dispersion forces.

Q: What is the difference between dipole-dipole interactions and hydrogen bonding?

A: Dipole-dipole interactions occur between polar molecules, where the positive end of one molecule is attracted to the negative end of another. Hydrogen bonding is a stronger type of intermolecular force that occurs between molecules that have a hydrogen atom bonded to a highly electronegative atom, such as oxygen, nitrogen, or fluorine. Hydrogen bonding is responsible for the high boiling points of substances like water and ammonia.

Q: Can you provide an example of how to calculate the boiling point of an alkane?

A: Yes, we can use the following formula to estimate the boiling point of an alkane:

Boiling Point (°C) = (Number of Carbon Atoms x 20) + (Number of Hydrogen Atoms x 10)

For example, let's calculate the boiling point of hexane (C6H14):

Boiling Point (°C) = (6 x 20) + (14 x 10) = 120 + 140 = 260°C

Q: How do you determine the order of increasing boiling point for a list of alkanes?

A: To determine the order of increasing boiling point for a list of alkanes, you need to consider the size of the molecules, the number of carbon atoms, and the arrangement of these atoms. Larger molecules with more carbon atoms tend to have higher boiling points due to stronger London dispersion forces. You can use the formula provided earlier to estimate the boiling point of each alkane and then arrange them in order of increasing boiling point.

Q: What are some common applications of alkanes in industry and everyday life?

A: Alkanes are widely used in various industrial and everyday applications, including:

Fuel: Alkanes are used as fuels in vehicles, power plants, and other industrial applications.
Lubricants: Alkanes are used as lubricants in engines, gears, and other mechanical systems.
Plastics: Alkanes are used as feedstocks for the production of plastics, such as polyethylene and polypropylene.
Cosmetics: Alkanes are used in cosmetics and personal care products, such as skin creams and hair care products.

Conclusion

In conclusion, the relationship between alkane structure and boiling point is a complex and fascinating topic. By understanding the factors that affect boiling point, such as the size of the molecule and the strength of intermolecular forces, we can predict the boiling point of an alkane and arrange a list of alkanes in order of increasing boiling point. We hope that this Q&A article has provided additional information and clarification on this topic, and we welcome any further questions or comments.