|Picture 2.2 How diffusion works. The blue particles move and mix with the red particles. Note: the real particles are not coloured.|
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| ||Explaining diffusion|
| || ||Diffusion is when two fluids mix together without any help from us. We can explain this using the idea that particles move. |
Instead of the particles moving around and mingling with particles of the same material, they move around and mingle with particles of the other material as well.
If you pour some water into a glass followed by some cola drink, the colour of the cola spreads through the whole liquid. The cola particles, which cause the colour, mingle with the water particles until they are all mixed together.
If the particles themselves weren't moving, then the two liquids wouldn't be able to mix on their own. We would have to stir them.
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| ||An example of diffusion|
| || ||We can see a gas diffusing using bromine. This is a brown liquid that vaporises easily. You can see some of the vapour in picture 2.3. It is still at the bottom of the tube. |
However, as time passes, the vapour will diffuse up the tube. The bromine particles are moving around randomly. Gradually, although they bump into the air particles, they will make their way to the top. It takes about 45 minutes for the tube to be filled with brown bromine vapour.
If there were no air in tube, then the bromine particles would not be obstructed. You can watch a QuickTime movie of this. Click to choose the file size:
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