Gas Laws Kinetic Molecular Theory

Properties of Gases – Kinetic Molecular Theory

The kinetic molecular theory is the cornerstone upon which the ideal gas laws are founded. The kinetic molecular theory is a theory that aims to explain the phenomena of gases at standard temperatures and pressures.

The Theory

First of all, the theory states that particles are in constant, random motion. These particles are moving extremely fast (unimaginably fast, in fact), and are travelling in straight lines. The particles undergo elastic collisions with one another, in which energy is conserved. The resultant motion of the particles is called “random walk”.

Boyle’s Law

Kinetic molecular theory provides a simple physical explanation of Boyle’s law – the law stating that pressure and volume are inversely proportional. As pressure increases, volume decreases or vice-versa. This makes sense. Think about the case of a balloon. As the balloon shrinks in size, the distance that the particles need to travel to collide with the walls of the balloon decreases, causing the particles to collide with the balloon more frequently. Thus, the pressure exerted by the gas on the balloon increases.

Charles’ Law

The law of Charles describes the direct proportionality between pressure and temperature. As particles in the gas increase in temperature, their kinetic energy increases, causing them to collide with greater force. In a fixed-size container, the pressure on the walls of the container will be higher, as the particles are colliding with it with more energy. Thus the pressure is increased.

Gay-Lussac’s Law

This subset of the ideal gas law describes how, in a variable-sized container, volume is directly proportional to temperature. As in the case of Charles’ law, the increase in temperature increases the force with which the particles collide. This, in turn, increases the force exerted on the container by the gas. In this case, the container will expand until an equilibrium is reached between the outer pressure and the inner pressure.


Kinetic molecular theory offers chemists a great model to describe the physical effects of gas laws. This valuable tool serves as a great mnemonic aid as well, for those people who think using a physical model. This theory also applies to chemical reactions, solutions, and just about every other chemical concept. A solid knowledge of kinetic molecular theory is a sure key to success in chemistry.