Question

Which of the following are pseudo unimolecular reactions:
This question has multiple correct options:
(A.) $C{{H}_{3}}COO{{C}_{2}}{{H}_{5}}+HOH\xrightarrow{{{H}^{+}}}C{{H}_{3}}COOH+{{C}_{2}}{{H}_{5}}OH$
(B.) $C{{H}_{3}}COO{{C}_{2}}{{H}_{5}}+HOH\xrightarrow{O{{H}^{-}}}C{{H}_{3}}COOH+{{C}_{2}}{{H}_{5}}OH$
(C.) ${{C}_{12}}{{H}_{22}}{{O}_{11}}+HOH\xrightarrow{{{H}^{+}}}{{C}_{6}}{{H}_{12}}{{O}_{6}}+{{C}_{6}}{{H}_{12}}{{O}_{6}}$
(D.) $S{{O}_{2}}C{{l}_{2\left( g \right)}}\to S{{O}_{2\left( g \right)}}+C{{l}_{2\left( g \right)}}$

Answer 1

Hint: We should know that a chemical reaction if two or more reactants are involved but the rate of reaction depends only upon the concentration of one of the reactants, is said to be the pseudo unimolecular reaction. Now, try to answer this question accordingly.

Complete Solution :
Let’s find the correct answer to this question.
- The first thing we need to know is that, A pseudo-first-order reaction can be defined as a second-order or bimolecular reaction that is made to behave like a first-order reaction.
It occurs when one reacting material is present in great excess or is maintained at a constant concentration compared with the other substance.
- So, we can say the reactions having molecularity two but the order of the reaction is one is called pseudo unimolecular reactions. In such types of reactions, one reagent is taken in the excess amount so that the disappearance of that reagent is negligible and it does not determine the rate of reaction.
 - Here, in options A, B, and C all the reactions are pseudo unimolecular as [${ H }_{ 2 }O$] is in the excess. So, the rate of reaction will be independent of the concentration of ${ H }_{ 2 }O$.
So, the correct answer is “Option A,B and C”.

Note: We should know that a first-order reaction is a reaction whose rate depends on the concentration of only one of the reactants.