The Ultimate Guide- Identifying the Compound with the Lowest Boiling Point Among the Options

Which of the following should have the lowest boiling point?

The boiling point of a substance is determined by the strength of the intermolecular forces between its molecules. These forces can be categorized into several types, including London dispersion forces, dipole-dipole interactions, and hydrogen bonding. In this article, we will explore which of the following substances should have the lowest boiling point and why.

1. Ethanol (C2H5OH)
2. Water (H2O)
3. Methane (CH4)
4. Ethane (C2H6)

To determine which of these substances has the lowest boiling point, we need to consider the types of intermolecular forces present in each. Let’s analyze each substance one by one.

1. Ethanol (C2H5OH)
Ethanol has a molecular mass of 46.07 g/mol and contains an oxygen atom, which can form hydrogen bonds with other ethanol molecules. Hydrogen bonding is a strong intermolecular force that requires a significant amount of energy to break, resulting in a higher boiling point. Therefore, ethanol should have a higher boiling point than substances without hydrogen bonding.

2. Water (H2O)
Water is well-known for its ability to form hydrogen bonds, which are even stronger than those in ethanol. The presence of two hydrogen atoms bonded to an oxygen atom allows water molecules to form extensive hydrogen bonding networks. This results in a much higher boiling point than ethanol, so water should not have the lowest boiling point among the substances listed.

3. Methane (CH4)
Methane is a nonpolar molecule composed of one carbon atom and four hydrogen atoms. Nonpolar molecules like methane only have London dispersion forces, which are the weakest type of intermolecular force. London dispersion forces arise from temporary fluctuations in electron density, creating temporary dipoles. These temporary dipoles can induce dipoles in neighboring molecules, leading to a weak attraction between them. Since methane has no hydrogen bonding or dipole-dipole interactions, it should have the lowest boiling point among the substances listed.

4. Ethane (C2H6)
Ethane is also a nonpolar molecule, similar to methane. It consists of two carbon atoms and six hydrogen atoms. Like methane, ethane only has London dispersion forces, making it a weaker intermolecular force compared to hydrogen bonding. However, ethane has a higher molecular mass than methane (30.07 g/mol vs. 16.04 g/mol), which means it has more electrons and a larger electron cloud. This results in stronger London dispersion forces, making ethane’s boiling point slightly higher than methane’s.

In conclusion, among the substances listed, methane (CH4) should have the lowest boiling point due to its nonpolar nature and the absence of stronger intermolecular forces like hydrogen bonding or dipole-dipole interactions.