The Kinetic Molecular Theory (KMT) is a theoretical model used to explain the observable properties of gases. The basis of KMT operates on three postulates or assumptions. They include:

• A gas is composed of particles.
  • These particles can be collections of atoms, like NH₃.
  • These particles can be atoms themselves, like He.
  • The particles of a gas are considered to be small, hard spheres whose physical presence occupies no volume (a gas's volume is due to its motion alone).
  • The particles experience no forces of attraction, or repulsion either between each other, or with the object that contains them.
• The particles in a gas move rapidly in constant random motion.
  • Each particle's motion is assumed to be linear and independent of any other particle.
• All collisions are perfectly elastic.
  • All energy is conserved between particles and between particles and the container.
  • Kinetic energy is conserved.

Gases that exist in our physical world are said to be real gases. When the assumptions of KMT are applied to real gases, those gases are said to be ideal. While many of the KMT assumptions are quantifiable, little is lost by making the assumptions. KMT defines the measurable gas variables as pressure, temperature, amount of gas, and volume.

This very well-developed applet provides an excellent two dimensional KMT model. You should experiment with this applet by varying the temperature and molar mass of the samples. You can see, side-by-side, how the changes affect the gas particle motions. Consider using this applet with your high school students -- either for a class demonstreation or as part of a lab assignment.

KMT Links

• Kinetic Molecular Theory Basics
• How gas laws explained [local]