Kinetic theory of an ideal gas
The kinetic theory of gases (also known as kinetic-molecular theory) is a law that explains the behavior of a hypothetical ideal gas. According to this theory, gases are made up of tiny particles in random, straight line motion.
They move rapidly and continuously and make collisions with each other and the walls. This was the first theory to describe gas pressure in terms of collisions with the walls of the container, rather than from static forces that push the molecules apart.
Kinetic theory also explains how the different sizes of the particles in a gas can give them different, individual speeds.
The kinetic theory of gases is the study of the microscopic behavior of molecules and the interactions which lead to macroscopic relationships like the ideal gas law.
An ideal gas is a gas where the atoms do not exert forces on each other but they do collide with the walls of the container (in elastic collisions).
Based on common sense and experiment the ideal gas law relates the pressure, temperature, volume, and number of moles of ideal gas:
PV = nRT,
where
R is a constant known as the universal gas constant.
The Kinetic Theory of Gases
Gases are made up of molecules:
We can treat molecules as point masses that are perfect spheres. Molecules in a gas are very far apart, so that the space between each individual molecule is many orders of magnitude greater than the diameter of the molecule.
Molecules are in constant random motion:
There is no general pattern governing either the magnitude or direction of the velocity of the molecules in a gas. At any given time, molecules are moving in many different directions at many different speeds.
The movement of molecules is governed by Newton’s Laws:
In accordance with Newton’s First Law, each molecule moves in a straight line at a steady velocity, not interacting with any of the other molecules except in a collision.
In a collision, molecules exert equal and opposite forces on one another.
Molecular collisions are perfectly elastic:
Molecules do not lose any kinetic energy when they collide with one another.