This theory state that matter is made up of tiny particles which are continuously moving.

Some important points to note o the kinetic theory are:

• All matter is made up of tiny moving particles which cannot be seen
• The particles are always moving
• The higher the temperature the faster the particles are moving
• Small particles move faster than larger particles

When solid is heated:

• Its particles gain kinetic energy, vibrate faster and turn to separate from each other to form a liquid.

When a liquid is heated:

• Its particles gain kinetic energy, move faster collide with one another to form a gas.
• The gas is cooled, its speed slows down and the particles stick together to form a liquid, while cooling continuously the liquid particles stick to form solid.

N.B: heating increases the kinetic energy of particles while cooling reduces it.