What is the Kinetic Particle Theory?

Learning Objectives:

1. Describe the solid, liquid and gaseous states of matter, and explain their inter-conversion in terms of the kinetic particle theory, and the energy changes involved.
2. Use models to understand the behaviour of particles in the three states of matter.
3. Compare and relate the characteristics of the three states of matter (solid, liquid and gas) in terms of the arrangement and movement of the particles.

A matter is defined as anything that has mass and occupies space, which can exist in 3 states – solid, liquid and gas.

Historically, the states of matter were distinguished based on qualitative differences in their physical properties.

A solid has a fixed volume and cannot be compressed, a fix shape and a high density. Similarly, a liquid have a fixed volume and hence cannot be easily compressed, but has no fixed shape with a lower density than the solids. A gas, on the other hand, has no fixed volume and can be compressed, has no fixed shape and has the lowest density out of the 3 states of matter.

Alternatively, these physical differences can be explained using the Kinetic Particle Theory (KPT). The KPT is a model which is used to explain the properties of the different states of matter on a microscopic level.

The KPT assumes that all matter are made up of tiny particles, which may be atoms, ions or molecules. Tiny spaces are found between the particles in the matter and these particles are always in continuous random motion (possess kinetic energy). Lighter particles should also move faster than heavier particles at the same temperature.