Catalysts and Catalysis
Catalysis is a chemical process in which the rate of a chemical reaction is either increased or decreased by the addition of a small quantity of a foreign substance that remains unchanged in mass and chemical composition at the end of the reaction. The added substance is known as a catalyst.
Types of Catalysts:
1. Positive Catalyst: When a catalyst increases the rate of a reaction, then it is called a positive catalyst, and the process is called positive catalysis.
2. Negative Catalyst: When a catalyst diminishes the rate of a reaction, it acts as a negative catalyst and the process is called negative catalysis.
3. Induced Catalyst: Here one reactant catalyzes the speed of the other reactant. A solution of sod Arsenite is not oxidized to sod. Arsenate on exposure to sir but sod. sulphate under the same condition. When a mixture of sod. arsenite and sod. sulphite is exposed to air both salts are simultaneously oxidized. It is called Induced Catalyst.
Types of Catalysis:
1. Autocatalysis: There are some reactions in which one of the products of the reactions acts as a catalyst. They are autocatalysts and the phenomenon is called autocatalysis.
2. Homogeneous Catalysis: When the reactants and catalysts are in the same phase, the catalysis is known as Homogeneous Catalysis.
3. Heterogeneous Catalysis: When the reactants and the catalysts are in different phases, the catalysis is known as heterogeneous catalysis.
4. Enzyme Catalysis: Many chemical reactions are catalyzed by complex organic substances called Enzyme Catalysis.