# How do you explain diffusion

In the diffusion (Latin: diffundere = to spread) is a passive process that describes the tendency of particles to distribute themselves evenly in a room. In this way, after a certain time, two different substances are always completely mixed (concentration equalization). The principle of diffusion applies to the mixing of gases as well as liquids, which is why the phrase "uniform distribution in space" must not be interpreted too narrowly. In principle, diffusion takes place everywhere.
To illustrate this process, it is sufficient to put ink into a water glass:

The ink slowly mixes with the water (Figure 2-3), until at the end there is only a homogeneous liquid (Figure 4).

The cause of the diffusion is the so-called "Random walk"of the particles, which one could also translate as" random movement ". You have to know that atoms and molecules are always moving on a molecular level. The warmer the ambient temperature, the faster the particles move. In this context, the Brownian molecular motion spoken (named after the discoverer Robert Brown). Only at a temperature of around -273.15 * C, the absolute zero point, the particles no longer move. Everyone has certainly experienced the influence of temperature on the mixing of two substances while cooking: Everything is easier to dissolve in hot water than in cold water.

The picture on the left shows the mixing of two different substances (gaseous) during diffusion. All particles move coincidentally and undirected in every possible direction. Particles collide with each other, causing constant changes of direction.
In the long term, these undirected movements of the particles lead to an equalization of the concentration of both substances, because apart from the direction-changing hits, there is no direct interaction between the particles. Each particle moves alone, independently and randomly in space, with the result that over time it comes to a mixture.

Diffusion is a stochastic process and can therefore be described using the calculus of probability. With the appropriate variables, it could be calculated how long it takes for both substances to mix completely.