Catalyst

In chemistry, a catalyst is a substance which increases the speed of a Chemical reaction; it takes part in the reaction but it forms part neither of the products, nor of the reagents and thus does not appear in the equation-assessment of this reaction.

The catalyst accelerates, sometimes in considerable proportions, the chemical reaction, but it is not consumed: either it does not take part in the reaction but its presence facilitates the rupture of the connections, or it takes part but is regenerated in it at the end.

The catalysts are largely used in industry and in Laboratoire.

In nature and in biochemistry, some Protéines have a catalytic activity. They acts of the Enzyme S.

The catalyst increases the reaction speed by introducing new ways of reaction (mechanism), and by lowering its energy of activation, or free energy of Gibbs of activation. By doing this it makes it possible to increase speed, or to lower the temperature of the reaction. The catalyst does not modify the free energy of Gibbs total of the reaction which is a function of state of the system and thus has no effect on the constant of balance.

In addition to increasing the reaction speed, the choice of a catalyst can rest on other parameters:

  • the selectivity : a selective catalyst will support the production of the product wished compared to the secondary products. For example, when one uses the metal money to catalyze the reaction of formation of oxide of ethylene, starting from oxygen and by ethylene, this reaction is accompanied by the more favorable formation thermodynamically by CO2 and H2O. For this reason it is important to find a catalyst supporting the desired product.

  • the lifespan , a small quantity of catalyst must be able to survive several cycles of reaction

Simple example of a catalyst:

Ash on sugar is a good catalyst: Try to light a sugar with a lighter. That made caramel as well as possible. Now, put a little ash on sugar, and try to light at the place where you put ash. sugar burns then with a non luminous flame, until there is no more that ash.

Various types of catalysts:

See too

Simple: Catalyst

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