Types of catalysts
Types of catalysts are listed below:
(i) Positive catalysts:
A catalyst which increases the rate of reaction is called positive catalyst. Such catalyst decreases activation energy by accepting a smaller path, so rate of reaction is increased.
(ii) Negative catalysts (Inhibitors):
A catalyst which decreases or retards the rate of reaction is called negative catalysts.
It is because a -ve catalyst increase activation energy by taking a longer alternative path.
(2) T.E.L (Tetra Ethyl Lead) an ant knocking substance is added to petrol to decrease the ignition of petrol vapours.
(3) Here acts as -ve catalyst to slow the oxidation .
(4) Acetanilide also acts as —ve catalyst in decomposition of
When one of the products formed in the reaction acts as a catalyst is known as auto-catalyst.
In this reaction acts as auto catalyst which is formed as a side reaction :
Auto catalysis reaction starts slowly in the beginning but as auto catalyst is formed rate of reaction starts increasing.
(iv) Induced catalyst:
The substance which influences the speed of other reaction, which is not possible under ordinary conditions, is known as induced catalyst.
Sodium sulphite solution readily oxidises in air, but sodium arsenite solution does not oxidise by passing air in the solution. When both these solutions are mixed and air is passed then both the substances get oxidised.
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