KINETIC THEORY of mater

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Diffusion    Brownian motion

The kinetic theory states that all matter is made up of tiny particles that are constantly moving.

Solid:
The particles are held closely together in a regular pattern and can only just vibrate
Liquid:
The particles are still close together but are now able to slide over one another and mix. The motion is more random than in a solid.

Gas:
The particles are far apart and able to move freely in straight lines.
They have a lot more kinetic energy than the particles in a solid or liquid.

The moving particles are responsible for causing substances to slowly mix together (see DIFFUSION) and for causing the pressure in a gas.

If a substance is warmed the particles will vibrate FASTER.

If the particles are smaller they will move faster

The link below demonstrates these points nicely:
Diagram to show the particles in a gas moving around and colliding

To use the animation in the link do the following

  1. Click on the link
  2.  Type a number of particles into the empty square near the top right (eg 100)
  3. Click 'set'
  4. Click 'Run'

The kinetic theory of gases can explain many observations:

eg 1. Brownian Motion
Brownian motion is the vibrating motion of a smoke particle (when smoke is viewed through a microscope).
It is caused by the fast moving are particles hitting the smoke particle and knocking it around.
Click here for demonstration of Brownian Motion

eg 2. Evaporation
The particles at the surface of a liquid have enough energy to break free and fly off into the air.

eg 3. Diffusion
Diffusion is the movement of one substance through another.
It happens rapidly in gases but slowly in liquids because the particles are much closer together.
Solids do not diffuse.

example1: If some little coloured sugar grains are sprinkled onto some cream and left overnight by the morning the colours would have started to spread out over the cream. This mixing of the colours is called diffusion.

example2: If the lid is taken off a perfume bottle the smell of the perfume will gradually spread around the room. This is due to the perfume molecules diffusing outwards.

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