An ideal gas, also known as a perfect gas, is a theoretical concept of a gas which would obey the gas laws exactly. Such a gas would consist of perfectly elastic molecules, the volume occupied by the actual molecules, and the forces of attraction between them, being zero or negligible.

 

In practice, no gas shows ideal behavior, although, helium, hydrogen, and nitrogen approximate to ideality at high temperatures and low pressures.

 

Ideal gas law

The ideal gas law is a law relating the pressure (P ), temperature (T ), and volume (V) of an ideal gas. Mathematically, the ideal gas law can be written as:

 

    pV = nRT,

 

where n is the number of moles of the gas present and R is the so-called gas constant.

 

The ideal gas law implies that at constant temperature (T ), the product of pressure and volume (pV ) is constant (Boyle's law) and at a constant pressure, the volume is proportional to the temperature (Charles' law). See also equation of state.