Question

In the reaction \[2S{{O}_{2}}+{{O}_{2}}\xrightarrow[A{{s}_{2}}{{O}_{3}}]{Pt}2S{{O}_{3}}\]​, \[A{{s}_{2}}{{O}_{3}}\] acts as a
A. Auto catalyst
B. Poison
C. Promoter
D. Positive catalyst

Answer 1

Hint: In a given reaction, along with reactants platinum is also has been added. This substance will increase the rate of reaction and release at the end of the reaction (on the product side). Thus, platinum is a catalyst whereas another reactant is also added to the creation which is \[A{{s}_{2}}{{O}_{3}}\] but it has just the opposite effect as compared to the catalyst, platinum.

Complete Step by Step Answer:
A catalyst provides active sites for reactants to attach to it. As soon as the reactant combines with the catalyst, the catalyst lowers the activation energy of the reaction. And thus we need to provide less energy to activate reactants to change to product easily and quickly.Platinum is also a catalyst and is added to a given reaction.

As per the hint, \[A{{s}_{2}}{{O}_{3}}\] has the opposite effect as platinum means that when platinum increases the rate of reaction it will decrease the rate of reaction, or can say it prohibits the activity of platinum catalyst.

The reagent \[A{{s}_{2}}{{O}_{3}}\], attacks the active site of the catalyst and there will be no active site left for the attack of the reactant on it. So, the catalyst cannot perform its work properly and cannot catalyse the reaction. When a substance attacks at active sites of a catalyst that prohibits the action of the catalyst or catalytic action, then that substance is known as poison.
Thus, the correct option is B.

Note: It is important to note that the promoter given in the option is a substance that enhances the activity or catalyst and thus increases the rate of reaction to a great extent. Also, it is not an auto catalyst and positive catalyst because when both auto catalyst and positive catalyst are added to a reaction they increase the rate of forward reaction or may also backward reaction in case of reversible reaction without being affected by the reaction and released at the end of the reaction.