reaction is taking place in a slow rate it can increase its rate. . A solid catalyst will be more effective if it is taken in a finely divided form. .
A catalyst can catalyse a particular type of reaction, hence they are said to be specific in nature. . In an equilibrium reaction, presence of catalyst reduces the time for attainment of equilibrium and hence it does not affect the position of equilibrium and the value of equilibrium constant. .
A catalyst is highly effective at a particular temperature called as optimum temperature. . Presence of a catalyst generally does not change the nature of products For example. 2SO +O 2SO This reaction is slow in the absence of a catalyst, but fast in the presence of Pt catalyst XII U10-Surface XII U10-Surface - - - - Promoters and catalyst poison In a catalysed reaction the presence of a certain substance increases the activity of a catalyst.
Such a substance is called a promoter. For example in the Haber’s process of manufacture of ammonia, the activity of the iron catalyst is increased by the presence of molybdenum. Hence molybdenum is called a promoter. In the same way Al O can also be used as a promoter to increase the activity of the iron catalyst.
On the other hand, certain substances when added to a catalysed reaction decreases or completely destroys the activity of catalyst and they are often known as catalytic poisons. Few examples, In the reaction, 2SO +O 2SO with a Pt catalyst, the poison is As O i.e., As O destroys the activity of Pt . As O blocks the activity of the catalyst. So, the activity is lost.
In the Haber’s process of the manufacture of ammonia, the Fe catalyst is poisoned by the presence of H S . In the reaction, 2H +O 2H O , CO acts as a catalytic poison for Pt - catalyst Auto catalysis In certain reactions one of the products formed acts as a catalyst to the reaction. Initially the rate