In order to simplify the understanding and the associated mathematics of the behavior of gasses, chemists have developed the concept of an "ideal gas". An ideal gas differs from real gasses in that they have specific properties which allows for the development of simple mathematical models for the behavior of gasses. These special properties include
ideal gas molecules never collide nor interact with each other in any way
ideal gas molecules never lose energy when they collide with the sides of their container
the molecules never stop moving
ideal gasses are infinitely compressible
These simplifications allow chemists to further develop the Kinetic-molecular theory. The KMT offers these properties of ideal gasses
gasses are made up of discrete molecules
gas molecules transfer force to their container walls which is measured as pressure
gas molecules have kinetic energy which is proportional to their mass and the speed of the molecules (following the kinetic energy equation)
the temperature of a gas measured in the Kelvin scale is proportional to the average kinetic energy of the molecules of the gas.
One nice thing about the KMT and ideal gasses is that many real gasses behave very much like ideal gasses at normal temperatures and pressures. Consequently, there is only a small error in analyzing gasses at room temperature and close to atmospheric pressure introduced by treating them as ideal.