Problem 12 - Chemistry: The Central Science in SI Units, Global Edition

Question

At room temperature, \(\mathrm{CO}_{2}\) is a gas, \(\mathrm{CCl}_{4}\) is a liquid, and \(\mathrm{C}_{60}\) (fullerene) is a solid. List these substances in order of (a) increasing intermolecular energy of attraction and (b) increasing boiling point.

Step-by-Step Solution

Answer

In terms of (a) increasing intermolecular energy of attraction and (b) increasing boiling point, the order is CO₂ < CCl₄ < C₆₀. CO₂ has the weakest London dispersion forces, followed by CCl₄, and C₆₀ with the strongest London dispersion forces. Consequently, CO₂ has the lowest boiling point, followed by CCl₄, and C₆₀ with the highest boiling point.

Step 1: CO₂ < CCl₄ < C₆₀

In terms of increasing intermolecular energy of attraction, it will be CO₂ (with the weakest London dispersion forces), followed by CCl₄, and finally C₆₀ (with the strongest London dispersion forces). #b. Increasing Boiling Point # The boiling point of a substance is directly related to its intermolecular forces. Stronger intermolecular forces lead to higher boiling points because more energy is needed to break the bonds between the molecules.

Step 2: CO₂ < CCl₄ < C₆₀

As CO₂ has the weakest intermolecular forces, it will have the lowest boiling point, followed by CCl₄, and then C₆₀ (with the strongest intermolecular forces) will have the highest boiling point.

Key Concepts

Boiling Point

The boiling point of a substance is the temperature at which its vapor pressure equals the external pressure surrounding the liquid, causing the liquid to turn into a gas.
This conversion requires energy to overcome the intermolecular forces holding the molecules together in the liquid state.

• Substances with stronger intermolecular forces will have higher boiling points because more energy is needed to separate the molecules.
• For example, in the original problem, \( ext{C}_{60} \) (fullerene), with the strongest intermolecular forces, has the highest boiling point.
• The sequence then is: \( ext{CO}_{2} \) < \( ext{CCl}_{4} \) < \( ext{C}_{60} \).

Understanding boiling points helps in predicting the physical state of a substance at a given temperature. It's a crucial factor in processes such as distillation and in explaining phenomena like why water boils faster at high altitudes.

London Dispersion Forces

London Dispersion Forces are the weakest type of intermolecular forces, also known as Van der Waals forces.
These forces occur between all atoms and molecules due to fluctuations in the electron cloud that create temporary dipoles.

• They are significant in nonpolar molecules where no permanent dipole exists.
• The strength of London Dispersion Forces increases with the size and mass of the molecule.
• In the original exercise, \( ext{CO}_{2} \) has the weakest London Dispersion Forces, whereas \( ext{C}_{60} \) has the strongest due to its larger size.

These forces are essential in understanding the relative volatility, boiling points, and solubility of nonpolar substances. While weak individually, London dispersion forces can be substantial when a molecule has a large surface area. They often determine the physical properties of substances, especially those that are nonpolar.

States of Matter

The states of matter — solid, liquid, and gas — are fundamentally determined by the strength of the intermolecular forces between their molecules.
Each state represents a different arrangement and motion of molecules.

• In solids, molecules are closely packed with strong intermolecular forces, keeping them in fixed positions.
• Liquids have intermediate intermolecular attractions, allowing their molecules to flow while still being relatively close.
• Gases have very weak intermolecular forces, with molecules far apart and moving freely.

In the exercise provided:
\( ext{CO}_{2} \) is a gas, indicating it has weak intermolecular forces;
\( ext{CCl}_{4} \) is a liquid with moderate forces; and \( ext{C}_{60} \) is a solid with strong intermolecular forces.
Understanding the states of matter is key to grasping how substances behave under different conditions, from everyday experiences to industrial applications.