Diffusion (Latin of diffusio – distribution, dispersion, spreading) is the phenomenon at which mutual penetration of molecules of different substances among themselves is observed, i.e. molecules of one substance get between molecules of another and vice versa.
Diffusion in everyday life
The phenomenon of diffusion can often be observed in everyday life of the person. So, if to bring in the room a source of any smell – for example, coffee or spirits – this smell will soon extend on all room. Dispersion of odorous substances happens because of continuous motion of the molecules. On the way they face molecules of the gases which are a part of air change the direction and, randomly moving, scatter on all room. Such distribution of a smell – the proof of chaotic and continuous motion of the molecules.
How to prove that bodies consist of continuously moving molecules
For the proof that all bodies consist of the molecules which are in the constant movement it is possible to conduct the following physical experiment. Pour in dark-blue solution of copper vitriol is rolled or a graduated cylinder. From above carefully flow clear water. In the beginning between liquids the sharp border will be visible, but in several days it will become indistinct. In few weeks the border separating water from solution of copper vitriol will disappear absolutely, and in a vessel uniform liquid of a pale blue shade is formed. It will tell you that liquids mixed up.
To explain the observed phenomenon, it is possible to assume that the molecules of copper vitriol and water located near an interface are interchanged the position. The border between liquids becomes indistinct as molecules of copper vitriol move to the lower water layer, and water molecules – in the top layer of blue solution. Gradually molecules of all these substances by the random and continuous motion extend on all volume, doing liquid uniform. This phenomenon is also called diffusion.
Whether there is a diffusion in solid bodies
In solid bodies the diffusion happens too, but much more slowly. So, if to put at each other smoothly ground plates of gold and lead and to press them cargo, in 4-5 years lead and gold mutually will get each other on 1 mm. Diffusion is here too observed.
What diffusion speed depends on
Speed of diffusion depends on temperature. At temperature increase the process of mutual penetration of substances accelerates. It is connected with the fact that when heating the general speed of motion of the molecules increases. The previous experience with gold and lead, for example, is carried out at the room temperature (20˚C), but in other conditions the results would be excellent.