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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For the reaction $2NOBr(g) \rightarrow 2NO(g) + Br_2(g)$, the rate law is $r = k[NOBr]^2$. If the rate constant $k = 1.62 \times 10^{-2} \text{ L mol}^{-1} \text{ s}^{-1}$ and the concentration of $[NOBr] = 2 \times 10^{-3} \text{ mol L}^{-1}$, what is the rate of reaction?
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View SolutionIn the presence of $HCl$,sucrose gets hydrolysed into glucose and fructose. The concentration of sucrose was found to reduce from $0.4 \ M$ to $0.2 \ M$ in $1 \ hour$ and to $0.1 \ M$ in $2 \ hours$. The order of the reaction is:
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View SolutionThe given data are for the reaction:
$2NO_{(g)} + Cl_{2(g)} \to 2NOCl_{(g)}$ at $298 \ K$
Experiment $[Cl_2] \ (M)$ $[NO] \ (M)$ Rate $(mol \ L^{-1} \sec^{-1})$ $I$ $0.05$ $0.05$ $1 \times 10^{-3}$ $II$ $0.15$ $0.05$ $3 \times 10^{-3}$ $III$ $0.05$ $0.15$ $9 \times 10^{-3}$
The rate law for the reaction is:
$2NO_{(g)} + Cl_{2(g)} \to 2NOCl_{(g)}$ at $298 \ K$
| Experiment | $[Cl_2] \ (M)$ | $[NO] \ (M)$ | Rate $(mol \ L^{-1} \sec^{-1})$ |
| $I$ | $0.05$ | $0.05$ | $1 \times 10^{-3}$ |
| $II$ | $0.15$ | $0.05$ | $3 \times 10^{-3}$ |
| $III$ | $0.05$ | $0.15$ | $9 \times 10^{-3}$ |
The rate law for the reaction is:
Medium
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