VIDEO: Degree of division in chemistry

Degree of division - an explanation of terms

• The degree of division of a substance indicates how large the surface is in relation to its volume. A sphere has a very low degree of division, a cube of the same volume a considerably larger one.
• In addition to the geometry the degree of division also depends on the size of the body. If you cut one cube into eight smaller ones, you don't change the volume, but the surface area doubles.
• In the chemistry reactions of two solids take place at the interface between these two substances. The higher the degree of division of a substance, the larger the surface on which reactions can take place and the faster the reaction takes place.
• A well-known example of this is the so-called flour dust explosion. If you hold ordinary household flour in front of an open flame, nothing happens at first - the degree of division of the flour is not sufficient. In a mill, however, there is much finer flour - the so-called flour dust. This flour dust has a very high degree of fragmentation and can explode if it comes into contact with an open flame.
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• Another example is the diesel engine, where the diesel is finely atomized during injection in order to achieve a high degree of division.


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• In experiments in chemistry, the decisive factor is the degree of division of the substances. A fine iron powder, for example, will react differently than a solid iron block.

Determination of the degree of division in chemistry

The degree of fragmentation is a qualitative measured variable, i.e. no exact numerical value can be given. There are, however, ways of specifying the degree of division.

• One of the most common methods is to separate a mixture by sieving it. Mesh sizes standardized in accordance with DIN66165 are used. After sieving, it is stated what the grain size distribution of the mixture is.
• Another possibility used in chemistry is to measure the volume and weight of the material. Since the density of the pure substance is known, it is possible to deduce from this how many gaps there are. The grain size distribution can also be inferred from this.
• This method can be further improved by comparing bulk volume with vibrating volume, since bulk goods have more air gaps than vibrating goods.