Medium
With the help of an example,explain what is meant by a pseudo first order reaction.
(N/A) reaction that is actually of higher order but follows first order kinetics under certain conditions is called a pseudo first order reaction.
This usually happens when one of the reactants is present in a large excess.
Example: The acid-catalyzed hydrolysis of ethyl acetate $(CH_3COOC_2H_5 + H_2O \xrightarrow{H^+} CH_3COOH + C_2H_5OH)$.
In this reaction,water is present in a large excess,so its concentration remains practically constant throughout the reaction.
The rate law is given by: $Rate = k[CH_3COOC_2H_5][H_2O]$.
Since $[H_2O]$ is constant,the rate becomes $Rate = k'[CH_3COOC_2H_5]$,where $k' = k[H_2O]$.
Thus,the reaction behaves as a first order reaction.
This usually happens when one of the reactants is present in a large excess.
Example: The acid-catalyzed hydrolysis of ethyl acetate $(CH_3COOC_2H_5 + H_2O \xrightarrow{H^+} CH_3COOH + C_2H_5OH)$.
In this reaction,water is present in a large excess,so its concentration remains practically constant throughout the reaction.
The rate law is given by: $Rate = k[CH_3COOC_2H_5][H_2O]$.
Since $[H_2O]$ is constant,the rate becomes $Rate = k'[CH_3COOC_2H_5]$,where $k' = k[H_2O]$.
Thus,the reaction behaves as a first order reaction.
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Similar Questions
For the elementary reaction $M \rightarrow N$,the rate of disappearance of $M$ increases by a factor of $8$ upon doubling the concentration of $M$. The order of the reaction with respect to $M$ is :
MediumIIT 2014
View SolutionWhich of the following statements is $NOT$ true for a reaction having rate law $r=k[H_2][I_2]$?
Select the rate law that corresponds to the data shown for the following reaction $A + B \to C$
$Expt. \ No.$ $[A]$ $[B]$ $Initial \ Rate$ $1$ $0.012$ $0.035$ $0.10$ $2$ $0.024$ $0.070$ $0.80$ $3$ $0.024$ $0.035$ $0.10$ $4$ $0.012$ $0.070$ $0.80$
| $Expt. \ No.$ | $[A]$ | $[B]$ | $Initial \ Rate$ |
|---|---|---|---|
| $1$ | $0.012$ | $0.035$ | $0.10$ |
| $2$ | $0.024$ | $0.070$ | $0.80$ |
| $3$ | $0.024$ | $0.035$ | $0.10$ |
| $4$ | $0.012$ | $0.070$ | $0.80$ |
DifficultAIIMS 2015
View SolutionFor the reaction $N_2O_5 \rightarrow 2NO_2 + \frac{1}{2} O_2$,given that:
$-\frac{d[N_2O_5]}{dt} = K_1[N_2O_5]$,
$\frac{d[NO_2]}{dt} = K_2[N_2O_5]$,
$\frac{d[O_2]}{dt} = K_3[N_2O_5]$
What is the relationship between $K_1$,$K_2$,and $K_3$?
$-\frac{d[N_2O_5]}{dt} = K_1[N_2O_5]$,
$\frac{d[NO_2]}{dt} = K_2[N_2O_5]$,
$\frac{d[O_2]}{dt} = K_3[N_2O_5]$
What is the relationship between $K_1$,$K_2$,and $K_3$?
Difficult
View SolutionThe rate law for the reaction,$NO_{2(g)} + CO_{(g)} \rightarrow NO_{(g)} + CO_{2(g)}$ is given as $R = k[NO_2]^2$. What is the order of reaction with respect to $CO$?
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