**ideal gas**is defined as one in which all collisions between atoms or molecules are

**perfectly elastic**and in which there are

**no intermolecular attractive forces**. An ideal gas can be visualized as a collection of perfectly hard spheres which collide but which otherwise do not interact with each other. In reality, no real gases are like an ideal gas and therefore no real gases follow the

**ideal gas law**or equation completely.

At temperatures near a gases boiling point, increases in pressure will cause condensation to take place and drastic decreases in volume. At very high pressures, the intermolecular forces of a gas are significant. However, most gases are in approximate agreement at pressures and temperatures above their boiling point. The **ideal gas law** is utilized by engineers working with gases because it is **simple to use** and approximates real gas behavior.

See also: Elastic Collision

## Equation of State

Any equation that relates the pressure, temperature, and specific volume of a substance is called an **equation of state**. The simplest and **best-known** equation of state for substances in the gas phase is the **Ideal Gas equation** of state.

*pV = nRT*

where:

is the*p***absolute pressure**of the gasis the*n***amount**of substanceis the*T***absolute temperature**is the*V***volume**is the ideal, or universal,*R***gas constant**, equal to the product of the Boltzmann constant and the Avogadro constant,

In this equation the symbol R is a constant called the **universal gas constant** that has the same value for all gases—namely, **R = 8.31 J/mol K.**