The kinetic theory of gases helps to explain the behaviour of gases based on the motion of the particles that compose them.
As a result of observations, in the 19th century scientists developed a theory to improve our understanding of the physical properties of gases. This theory, called the kinetic theory of gases, is based on the motion of the particles that make up a given gas. It provides a particle-level explanation of gas behaviour as well as the various laws that have subsequently been developed.
The kinetic energy of molecules in the gas phase is quite high, allowing the molecules to have a lot of motion. Thus, there are three types of molecular motion in gases:
|
Motion |
Description |
State of matter under which motion occurs |
|
Translation |
Motion of the molecule when it moves in a straight line in space. |
Much translational motion is found in gases, while none are observed in solids and very few in liquids. |
|
Rotation |
Motion of the molecule rotating on itself. |
Many rotational motions are found in gases, whereas this type of motion is non-existent in the solid state and weakly expressed in the liquid state. |
|
Vibration |
Motion of atoms of a molecule that vibrate around the centre of mass of that molecule. |
Many vibrational motions are found in gases and liquids, and few in solids. |
The molecular kinetic model is a scientific theory that applies to gases. It describes gases as being made up of particles that are constantly in motion, without any loss of energy.
Here is the most important thing to keep in mind about this theory:
- Gases are made up of microscopic particles. The distance separating these particles is enormous compared to the size of the particles involved.
- These particles move continuously in a straight line and in all directions.
- These particles continually collide and hit the walls of the container in which they are contained. All collisions occur without loss of energy (elastic collision).
- The kinetic energy of the translational motion of these particles is relative to the absolute temperature. The average kinetic energy of the particles of any gas is therefore identical at the same temperature.
All gases are characterized by the physical properties stated above even though their chemical properties differ greatly. Kinetic theory can explain most of the physical behaviours of gases.