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# What do you mean by activity and selectivity of catalysts?

5.20    What do you mean by activity and selectivity of catalysts?

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(i)The activity of the catalyst is to increase the rate of a particular reaction. It depends on the strength of chemisorption to a large extent. Adsorption of reactants should be neither too high nor too weak. It should just be optimum so that the catalyst is staying active.

(ii)The selectivity of catalyst is the ability to direct the reaction to give a particular product when under the same reaction condition the products are possible also.

Example- Reaction between CO and $H_{2}$

$\\(1)CO(g)+3H_{2}(g)\overset{Ni}{\rightarrow}CH_{4}(g)H_{2}O(g)\\ (2)CO(g)+2H_{2}(g)\overset{Cu/ZnO-Cr_{2}O_{3}}{\rightarrow}CH_{3}OH(g)\\ (3)CO(g)+H_{2}(g)\overset{Cu}{\rightarrow}HCHO(g)$

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