Consider the following reaction mechanism for the formation of nitrobenzene. Alright so identify the reaction intermediate or intermediates and catalysts or catalysts. So here if we take a look all of this together represents our reaction mechanism. Let's each individual reaction represents our elementary step, right? So here this would be elementary step one. This would be elementary Step 2 and elementary Step 3.
All right. So remember, a reaction intermediate appears first as a product, then later as a reactant. So if we take a look here, let's try to find them. Let's see. So here H2N3 appears as a product, and then later we see it appear as a reactant. So that would definitely be a reaction intermediate. But is that the only one? We would say no, that's not the only one. Who else does that? Here's another C6H6N2 plus here C6H6N2 plus here that is also a reaction intermediate. It appears first as a product and later as a reactant.
Do we see any others? Yes, we see this HSO4 minus appears as a product and then later as a reactant. Now do we have any catalysts? If we look, we do remember catalysts will appear in the very first step as a reactant, then it will appear in the very last elementary step as a product. So here this would be our catalyst and that would be our only catalyst involved in this entire reaction mechanism.
So just keep in mind a reaction intermediate appears first as a product and then later as a reactant. A catalyst appears as one of the first reactants, and then later in the very last elementary step, it appears as one of the products. So as long as you can remember that there was a difference between a reaction intermediate and a tablet.