States of Matter and Particle Theory   (Part 2)

Particle Theory


Diffusion

The movement of particles is called Diffusion. Gases diffuse quickly because the particles are moving quickly in all directions. Another definition of Diffusion is the movement of particles from an area of high concentration to areas of low concentration.

Consider how perfume or aftershave works. Initially particles of the perfume are sprayed into the air. Because the perfume and the air are both gases, the particles are moving very fast and bumping into each other. This causes the particles to move further in all different directions and hence the smell (perfume particles) to diffuse through the air all the way to your nose which is when you smell the perfume.

Expansion

When particles are heated, they become more active and move around more. It is important to note that the particles do not become larger themselves; they just take up more space as they are moving around a lot more. This is why all states of matter expand upon heating.
The degrees of expansion are dependent on the specific state. For example, solids will expand the least because the particles are held quite tightly together. Liquids will expand more than solids but Gases will expand the most. When cooled, substances contract and become smaller.

Expansion can exert a lot of force and in hotter countries this is taken into account when building. For example concrete roads are built with gaps in them to allow expansion in hot weather.

Gas Pressure

Gas particles move very quickly in all directions. If gas is in a container these gas particles will crash into the walls and this force creates gas pressure. If the temperature increases so does the activity of the gas particles and hence the gas pressure also increases.

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