Catalysis is homogeneous and heterogeneous catalysis: we explain by examples

Some chemical interactions in themselves occur very difficult or do not occur at all. And then special substances - catalysts - come to the aid. They allow to "bypass the barrier" - and the reaction begins, although without them it would either never began or would have occurred very slowly. Catalyzes homogeneous and heterogeneous catalysis. What do these words mean?

The name can be different depending on whether the catalyst and reagents are in one phase. The catalyst itself is not consumed in the reaction. If you see two phases with a boundary between the substance and the catalyst, the catalysis will be heterogeneous. The same can be said about the case when the aggregate state of matter and catalyst differ. Homogeneous occurs in a homogeneous medium, in a single phase.

In case of heterogeneous catalysis, the catalyst is often a solid, and the reagents are either liquids, or dissolved in liquids, or are gases. In this case, the reagents are adsorbed on the active catalyst centers (do not confuse adsorption and absorption.) The former means a kind of "gluing" to the surface, the second is when one substance penetrates the structure of the other).

There is a chemical interaction between the molecules of the reagent and the catalyst. It can include both the chemical reaction on the surface and the weakening of bonds within the molecules of the reagent. Then a reaction takes place, in which often the molecules of the remaining substance hit the molecules of the first reagent. The result of the reaction is desorbed, "peeled off" from the active centers. As already mentioned, the catalyst is not consumed in the reaction. Only the quantity of reagents and products changes.

Catalysis homogeneous and heterogeneous catalysis is widely used in industry. We give an example of the second, since we have already considered it theoretically.

As you know, margarine - saturated fat. It is solid in consistency. And vegetable fats, from which it is produced, are mostly liquid. How to achieve firmness? By hydrogenation, that is, the double bonds of carbon atoms become single due to the addition of hydrogen atoms. And as the catalyst acts metal nickel in a solid state. Fats, which are obtained in this reaction, are called hydrogenated. Of course, like all saturated fats, they are not very useful, but demonizing them is also not worth it.

Catalysis homogeneous and heterogeneous catalysis must be understood, since they help explain not only industrial but also natural processes. For example, the destruction of the ozone layer is an example of homogeneous catalysis.

Ozone is destroyed and created again by exposure to ultraviolet irradiation molecules. However, the normal process is disturbed in the presence of chlorine and fluorocarbon molecules, which are present in the atmosphere in the form of gases and are products of industrial emissions. What happens in this case? Molecules of chlorine and fluorine compounds of carbon collide with ozone molecules and take one oxygen atom from them. Then a compound of, say, chlorine with oxygen collides with another ozone molecule, resulting in an oxygen molecule and a regenerated chlorine compound that can further destroy thousands of ozone molecules. Thus, homogeneous catalysis occurs. As you can see, the knowledge of this process allows us to understand that one must be careful with the use of certain deodorants and liquids for refrigerators.

However, it should be noted that substances that catalyze homogeneous and heterogeneous catalysis can not only accelerate the reaction, but also slow it down. In this case, they are called inhibitors. And any catalysts, in turn, can be affected by certain substances: accelerators or poisons for the catalyst. Therefore, the catalysis process is multistage, and for its understanding it is necessary to understand the causes of catalysis. And it happens because in this process less activation energy is needed , because the process goes on a different path than if it went by itself.

As we have seen, examples of catalysis can be very different in favor of man. However, in order to change the world, you need to understand it. Therefore, study chemistry, not only "vpoglyadku."