Chapter 7: Problem 34

Long-chain hydrocarbon molecules of the type \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{20} \mathrm{CH}_{3}\) are solids and are used for things like waxes. The CH bonds are essentially nonpolar. Why are waxes solid at room temperature?

Short Answer

Expert verified

Waxes, consisting of long-chain hydrocarbon molecules like \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{20} \mathrm{CH}_{3}\), are solid at room temperature due to the presence of dispersion forces between the molecules. Although these forces are weak, the large size and length of the hydrocarbon chains result in a significant number of intermolecular interactions that contribute to the solidity of the substance at room temperature. These forces help to keep the molecules together in a solid form despite the nonpolar nature of their individual bonds.

Step by step solution

Identify the given molecule structure

In the given exercise, we have a hydrocarbon molecule represented by the formula: \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{20} \mathrm{CH}_{3}\). This molecule consists of a chain of carbon and hydrogen atoms, where each carbon atom is connected to two hydrogen atoms, except for the terminal carbons which are connected to three hydrogen atoms. This structure represents a long-chain hydrocarbon.

Determine the nature of the bonds in the molecule

Since the given hydrocarbon molecule consists of carbon and hydrogen atoms, the bond between the carbon and hydrogen is a nonpolar covalent bond. This is because the electronegativity difference between these two atoms is relatively small, resulting in a fairly even distribution of electron density in the bond.

Analyze the intermolecular forces present in the compound

As the CH bonds in the molecule are essentially nonpolar, we should focus on the other types of intermolecular interactions in the compound. The main types of intermolecular forces include dipole-dipole interactions, hydrogen bonding, and dispersion (London) forces. Since the hydrocarbon molecule does not have polar bonds or groups that can form hydrogen bonds, the only possible type of intermolecular force present is dispersion force.

Understand the role of dispersion forces in the compound's state

Dispersion forces, also known as London forces or van der Waals forces, are weak forces caused by temporary dipoles created by the movement of electrons around the nucleus of atoms. These temporary dipoles can induce other temporary dipoles in neighboring molecules, resulting in attractive forces between the molecules. Although these forces are weaker compared to other types of intermolecular forces, they could play a significant role in determining the state of matter for a substance, especially for large molecules.

Conclude why waxes are solid at room temperature

Waxes, which consist of long-chain hydrocarbon molecules, are solid at room temperature because of the dispersion forces between the molecules. Though these forces are weak, the large size and length of these hydrocarbon chains result in a significant number of intermolecular interactions and, therefore, contribute to the solidity of the substance at room temperature. These forces help to keep the molecules together in a solid form despite the nonpolar nature of their individual bonds.

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Long-chain hydrocarbon molecules of the type \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{20} \mathrm{CH}_{3}\) are solids and are used for things like waxes. The CH bonds are essentially nonpolar. Why are waxes solid at room temperature?

Short Answer

Step by step solution

Identify the given molecule structure

Determine the nature of the bonds in the molecule

Analyze the intermolecular forces present in the compound

Understand the role of dispersion forces in the compound's state

Conclude why waxes are solid at room temperature

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