Question

What is pseudo unimolecular reaction and write one example

Answer 1

Consider the following acid catalysed reaction: 

Hydrolysis of ethyl acetate: 

CH₃COOC₂H₅ + H₂O + H⁺→CH₃COOH + C₂H₅OH 

The above reaction is bimolecular but is found to be of first order, as experimentally it is observed that: The rate of reaction proportional to  [CH₃COOC₂H₅] only. 

The reason for such a behavior is that water is present in such a large excess that its concentration remains almost constant during the reaction. 

Such reactions which are not truly of the first order but under certain conditions become reactions of the first order are known as pseudo unimolecular reactions.