# Pseudo Unimolecular Reaction

The reactions having molecularity $\geq 2$ but order of reaction is one are called pseudo unimolecular reactions.

E g.

(i)         $CH_3COOC_2H_5 + H_2O \to CH_3COOH + C_2H_5OH \\[3mm] \text{Rate} = k[CH_3COOC_2H_5]$

Thus order of reaction is one but molecularity of the reaction is two.

(ii)      $C_{12}H_{22}O_{11} + H_2O \to C_6H_{12}O_6 + C_6H_{12}O_6 \\[3mm] \text{Rate} = k[C_{12}H_{22}O_{11}]$

Thus order of reaction is one but molecularity of reaction is two.

(iii)     $(CH_3CO)_2O + 2C_2H_5OH \to 2CH_3COOC_2H_5 + H_2O \\[3mm] \text{Rate} = k[(CH_3CO)_2O]$

Thus order of reaction is one but molecularity of reaction is three.

Similarly the reactions having molecularity $\geq 3$ but order of reaction is two are called pseudo bimolecular reactions.

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