Explain Pseudo first order reaction with example. - Vidyadip

Question

Explain Pseudo first order reaction with example.

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Answer

→ The order of a reaction is sometimes altered by conditions.
→ There are many reactions which obey first order rate law although they are higher order reactions.
→ Consider the hydrolysis of ethyl acetate which is a chemical reaction between ethyl acetate and water. In reality, it is second order reaction and concentration of both ethyl acetate and water affect the rate of the reaction.
→ But water is taken in large excess for hydrolysis therefore, concentration of water is not alter much during the reaction.
→ Thus, the rate of reaction is affected be concentration of ethyl acetate.
→ For e.g. 0.01 mol ethyl acetate react with 10 mol of water amounts of the reactants and products at the beginning (t = 0) and completion (t) the reaction are give as under.

The concentration of water does not get altere much during the course of the reaction. So, the reaction behaves as first order reaction. Such reactions are called pseudo first order reactions Inversion of cane sugar is another pseudo finy order reaction.
$\begin{array}{l} C _{12} H _{22} O _{11}+ H _2 O \xrightarrow{ H ^{\prime}} C _6 H _{12} O _6+ C _6 H _{12} O _6 \\ \text { cane sugar $\quad$$\quad$$\quad$$\quad$$\quad$Glucose $\quad$ Fructose } \\ \text { Rate }= k \left[ C _{12} H _{22} O _{11}\right] \\\end{array}$

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