Diffusion
What diffusion is, why particles spread from high to low concentration, how temperature and particle mass change the speed, the ammonia and hydrogen chloride tube, and Brownian motion. With Vietnamese subtitles. A “Check yourself” section with typed questions is below the video on the site.
Practice
- Check yourself: Diffusion – Type the missing words, put the steps in order and write a short answer. No multiple choice: you have to remember it.
Transcript
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. Concentration means how many particles there are in a space.
Each particle moves in a random direction. But there are more particles on the crowded side. So, overall, they spread out until they are evenly mixed.
Diffusion happens faster when the temperature is higher. The particles have more energy and they move faster.
Diffusion is also faster for lighter particles. Heavier particles move more slowly.
Here is a famous experiment. Cotton wool with ammonia is at one end of a glass tube. Cotton wool with hydrogen chloride is at the other end. Both are gases.
The two gases diffuse along the tube. When they meet, they react and make a white ring of ammonium chloride.
The ring forms closer to the hydrogen chloride end. Ammonia is lighter, so it diffuses faster and travels further.
Now look at smoke in air through a microscope. The smoke particles move in a random, zigzag way. This is called Brownian motion.
The air particles are too small to see. But they move fast and keep hitting the smoke particles from all sides. This makes the smoke particles move.
Remember. Diffusion is the net movement of particles from high concentration to low concentration. It is faster when it is hot. It is faster for lighter particles. And Brownian motion is caused by moving particles hitting bigger ones.
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