NCERT Class XII Chemistry
Chapter - Surface Chemistry
Questions with Solutions
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Question : 20
Total: 35
What do you mean by activity and selectivity of catalysts?
Solution:
(a) Activity : The activity of a catalyst depends upon the strength of chemisorption to a large extent. The reactants must get adsorbed reasonably strongly on to the catalyst to become active. But adsorption must not be so strong that they areimmobilised. It is observed that maximum activity is shown by elements of groups 7-9 of the periodic table e . g , 2 H 2 + O 2
2 H 2 O
Selectivity : The selectivity of a calatyst is its ability to yield aparticularproduct in the reaction e.g.,
C O + 3 H 2
C H 4 + H 2 O
C O + 2 H 2
C H 3 O H
C O + H 2
H C H O
Thus,a selective catalyst can act as a catalyst in one reaction and may failto catalyse another reaction.
Selectivity : The selectivity of a calatyst is its ability to yield aparticularproduct in the reaction e.g.,
Thus,a selective catalyst can act as a catalyst in one reaction and may failto catalyse another reaction.
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