# 4: Gases

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• 4.1: The Perfect Gas
One way to begin to describe the nature of matter is to make a simplified, idealized model. The perfect gas is one such idealized model. In a perfect gas (or ideal gas), there are no interactions among the particles, which themselves have no volume. In this section it will be shown how a sample of idealized gas particles trapped in a container can be described by the perfect gas law, using the four variables of pressure, temperature, the number of gas particles, and the volume of the container.
• 4.2: Real Gases (Deviations From Ideal Behavior)
Real gas molecules have volume and experience intermolecular forces, and so are not accurately described by the perfect gas law. However, the perfect gas law can be modified to take into account the non-ideality of real gases. In this section we will describe how the characteristics of real gases cause their non-ideality, and then derive the modified gas laws.
• 4.3: van der Waals and Redlich-Kwong Equations of State
The van der Waals Equation of State is an equation relating the density of gases and liquids to the pressure, volume, and temperature conditions. The Redlich–Kwong equation of state is an empirical, algebraic equation that relates temperature, pressure, and volume of gases. It is generally more accurate than the van der Waals equation and the ideal gas equation at temperatures above the critical temperature.
• 4.4: The Law of Corresponding States
An additional assumption about real gases made by van der Waals was that all gases at corresponding states should behave similarly. The corresponding state that van der Waals choose to use is called the reduced state, which is based on the deviation of the conditions of a substance from its own critical conditions.
• 4.5: The Repulsive Term in the Lennard-Jones Potential
Proposed by Sir John Edward Lennard-Jones, the Lennard-Jones potential describes the potential energy of interaction between two non-bonding atoms or molecules based on their distance of separation. The potential equation accounts for the difference between attractive forces (dipole-dipole, dipole-induced dipole, and London interactions) and repulsive forces.

4: Gases is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.