Boiling Points and Intermolecular Forces

Oct 13, 2025 by thesweetdesigns.com 118 views

Intermolecular Forces and Boiling Points: A Comparative Analysis

When it comes to understanding the properties of substances, intermolecular forces play a crucial role. These forces are responsible for the physical and chemical properties of molecules, including their boiling points. In this article, we will explore the relationship between intermolecular forces and boiling points, and use this knowledge to determine which of the given options would have the highest boiling point.

What are Intermolecular Forces?

Intermolecular forces are the attractive and repulsive forces that act between molecules. These forces can be classified into several types, including:

London Dispersion Forces (LDFs): These are the weakest type of intermolecular force and arise due to temporary dipoles that form in non-polar molecules.
Dipole-Dipole Forces: These forces occur between polar molecules and arise due to the interaction between the positive end of one molecule and the negative end of another.
Hydrogen Bonding: This is a type of dipole-dipole force that occurs between molecules that have a hydrogen atom bonded to a highly electronegative atom, such as oxygen, nitrogen, or fluorine.

Boiling Points and Intermolecular Forces

The boiling point of a substance is the temperature at which the vapor pressure of the substance equals the surrounding atmospheric pressure. In other words, it is the temperature at which the substance changes state from a liquid to a gas. The boiling point of a substance is influenced by the strength of the intermolecular forces between its molecules.

Stronger intermolecular forces require more energy to overcome, which means that a substance with stronger intermolecular forces will have a higher boiling point. Conversely, a substance with weaker intermolecular forces will have a lower boiling point.

Comparing the Options

Now that we have a good understanding of intermolecular forces and their relationship to boiling points, let's compare the options:

A. $H_2$ : Hydrogen gas is a non-polar molecule, which means that it only experiences London Dispersion Forces. These forces are relatively weak, so we would expect $H_2$ to have a low boiling point.
B. $NH_3$ : Ammonia is a polar molecule that experiences dipole-dipole forces. Additionally, it has a hydrogen atom bonded to a nitrogen atom, which allows it to form hydrogen bonds with other ammonia molecules. These forces are stronger than London Dispersion Forces, so we would expect $NH_3$ to have a higher boiling point than $H_2$ .
C. $N_2$ : Nitrogen gas is a non-polar molecule that only experiences London Dispersion Forces. These forces are relatively weak, so we would expect $N_2$ to have a low boiling point.
D. $CH_4$ : Methane is a non-polar molecule that only experiences London Dispersion Forces. These forces are relatively weak, so we would expect $CH_4$ to have a low boiling point.

Based on our analysis of intermolecular forces and their relationship to boiling points, we can conclude that:

$NH_3$ would have the highest boiling point due to the presence of hydrogen bonds and dipole-dipole forces.
$H_2$ , $N_2$ , and $CH_4$ would have lower boiling points due to the presence of only London Dispersion Forces.

Atkins, P. W., & De Paula, J. (2010). Physical chemistry (9th ed.). Oxford University Press.
Chang, R. (2010). Chemistry: The central science (11th ed.). McGraw-Hill.
Levine, I. N. (2012). Physical chemistry (6th ed.). McGraw-Hill.

Substance	Boiling Point (K)
$H_2$	20.4
$NH_3$	240.6
$N_2$	77.4
$CH_4$	111.7

Note: The boiling points listed are for the substances at standard pressure (1 atm).
Intermolecular Forces and Boiling Points: A Q&A Guide

In our previous article, we explored the relationship between intermolecular forces and boiling points. We discussed how the strength of intermolecular forces affects the boiling point of a substance and used this knowledge to determine which of the given options would have the highest boiling point. In this article, we will answer some frequently asked questions about intermolecular forces and boiling points.

Q: What are the different types of intermolecular forces?

A: There are three main types of intermolecular forces:

London Dispersion Forces (LDFs): These are the weakest type of intermolecular force and arise due to temporary dipoles that form in non-polar molecules.
Dipole-Dipole Forces: These forces occur between polar molecules and arise due to the interaction between the positive end of one molecule and the negative end of another.
Hydrogen Bonding: This is a type of dipole-dipole force that occurs between molecules that have a hydrogen atom bonded to a highly electronegative atom, such as oxygen, nitrogen, or fluorine.

Q: How do intermolecular forces affect the boiling point of a substance?

A: The strength of intermolecular forces affects the boiling point of a substance. Stronger intermolecular forces require more energy to overcome, which means that a substance with stronger intermolecular forces will have a higher boiling point. Conversely, a substance with weaker intermolecular forces will have a lower boiling point.

Q: What is the difference between a polar and a non-polar molecule?

A: A polar molecule is a molecule that has a permanent electric dipole moment, meaning that it has a slightly positive charge on one end and a slightly negative charge on the other end. A non-polar molecule, on the other hand, is a molecule that has no permanent electric dipole moment.

Q: What is hydrogen bonding?

A: Hydrogen bonding is a type of dipole-dipole force that occurs between molecules that have a hydrogen atom bonded to a highly electronegative atom, such as oxygen, nitrogen, or fluorine. This type of bonding is particularly strong and is responsible for the high boiling points of substances such as water and ammonia.

Q: Can you give an example of a substance that exhibits hydrogen bonding?

A: Yes, water (H2O) is a classic example of a substance that exhibits hydrogen bonding. The oxygen atom in water is highly electronegative, which means that it pulls the shared electrons in the covalent bond between oxygen and hydrogen towards itself, creating a partial positive charge on the hydrogen atom. This partial positive charge is attracted to the partial negative charge on the oxygen atom of another water molecule, forming a hydrogen bond.

Q: What is the boiling point of water?

A: The boiling point of water is 373 K (100°C) at standard pressure.

Q: Can you give an example of a substance that exhibits London Dispersion Forces?

A: Yes, nitrogen gas (N2) is a classic example of a substance that exhibits London Dispersion Forces. Nitrogen gas is a non-polar molecule, which means that it only experiences London Dispersion Forces. These forces are relatively weak, which is why nitrogen gas has a low boiling point of 77.4 K (-195.8°C).

Q: What is the boiling point of nitrogen gas?

A: The boiling point of nitrogen gas is 77.4 K (-195.8°C) at standard pressure.

In this article, we have answered some frequently asked questions about intermolecular forces and boiling points. We have discussed the different types of intermolecular forces, how they affect the boiling point of a substance, and given examples of substances that exhibit each type of force. We hope that this article has been helpful in understanding the relationship between intermolecular forces and boiling points.

Atkins, P. W., & De Paula, J. (2010). Physical chemistry (9th ed.). Oxford University Press.
Chang, R. (2010). Chemistry: The central science (11th ed.). McGraw-Hill.
Levine, I. N. (2012). Physical chemistry (6th ed.). McGraw-Hill.

Substance	Boiling Point (K)
$H_2$	20.4
$NH_3$	240.6
$N_2$	77.4
$CH_4$	111.7
$H_2O$	373
$N_2$	77.4

Note: The boiling points listed are for the substances at standard pressure (1 atm).