Several properties of a gaseous sample can be explained readily by the features of a model of gas behavior called the kinetic-molecular theory or simply kinetic theory. This theory views the molecules as very small, very hard spheres that travel constantly and randomly at high speed.

Although scientists now think of kinetic-molecular theory as a very simple model of the behavior of atoms and molecules in the gas phase, it took over one hundred years for it to be accepted by the scientific community. Daniel Bernoulli (1700-1782) published an article describing a theory on this subject in 1743. However, it wasn't until the latter half of the next century that a statistical view developed by James Clerk Maxwell and Ludwig Boltzmann convinced physicists and chemists that individual molecules in a gas could be viewed as independent, rapidly moving bodies.

The kinetic molecular theory is important...