116.
What do you mean by activity and selectivity of catalysts?
Answer:
Activity of a catalyst. The ability of a catalyst to increase the rate of a particular reaction is called, catalytic activity. Chemisorption is the main factor in deciding the activity of a catalyst. The catalyst tungsten increases the rate of decomposition of ammonia to the extent of 1032 times which is otherwise slow process. The activity of a catalyst become more significant in the formation of water. Hydrogen and oxygen can be stored for years but not even a single drop of water will be produced in the absence of a catalyst. However, in the presence of platinum catalyst hydrogen and oxygen combine with explosion and form water.
Selectivity of a catalyst: The ability of a catalyst to affect only the desired reaction and to prevent any other side reaction is referred to as the selectivity of a catalyst. For example, both the dehydrogenation and dehydration of ethanol are possible. But in the presence of a suitable catalyst only one reaction occurs. Thus
(i) when nickel is ‘used as a catalyst, only dehydrogenation of ethanol occurs.
(
ii) When alumina (Al2O3) is used as catalyst only dehydration of ethanol occurs.
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