With the help of an example, explain what is meant by a pseudo-first-order reaction.
With the help of an example, explain what is meant by a pseudo-first-order reaction.
Pseudo-first-order reaction
A reaction which appears to be second-order reaction but is actually a first-order reaction is called a pseudo-first-order reaction.
This condition occurs in a chemical reaction between two substances, when one of the reactants is present in a large amount. The concentration of the reactant present in excess does not get altered much during the reaction. So, it behaves as a first-order reaction.
Example
Hydrolysis of esters.
Reaction –
CH3COOC2H5+H2O→CH3COOH+C2H5OH
Ethyl ethanoate Ethanoic acid Ethanol
Rate of reaction =
k[CH3COOC2H5][H2O]
But if [H2O]>>>[CH3COOC2H5]
Concentration of water will remain almost constant during the reaction.
Therefore, rate of the reaction
=k′[CH3COOC2H5]
Where, K′=k[H2O]
Thus, hydrolysis of ester is a
pseudo -first-order reaction.
Pseudo-first-order reaction
A reaction which appears to be second-order reaction but is actually a first-order reaction is called a pseudo-first-order reaction.
This condition occurs in a chemical reaction between two substances, when one of the reactants is present in a large amount. The concentration of the reactant present in excess does not get altered much during the reaction. So, it behaves as a first-order reaction.
Example
Hydrolysis of esters.
Reaction –
CH3COOC2H5+H2O→CH3COOH+C2H5OH
Ethyl ethanoate Ethanoic acid Ethanol
Rate of reaction =
k[CH3COOC2H5][H2O]
But if [H2O]>>>[CH3COOC2H5]
Concentration of water will remain almost constant during the reaction.
Therefore, rate of the reaction
=k′[CH3COOC2H5]
Where, K′=k[H2O]
Thus, hydrolysis of ester is a
pseudo -first-order reaction.
