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Explain pseudo first order reaction with an example. |
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Answer» Solution :Pseudo first order reaction : (i) Kinetic STUDY of a HIGHER order reaction is difficult to FOLLOW, for example, in a study of a second order reaction involving two DIFFERENT reactants , the simultaneous measurement of change in the concentration of both the reactants is very difficult. (ii)To overcome such difficulties, A second order reaction can be altered to a first order reaction by taking one of the reactant in large excess, such reaction is called pseudo first order reaction. (iii) Let us consider the acid hydrolysis of an ester, `CH_(3)COOCH_(3(aq))+H_(2)O_((l))overset(H^(+))rarr CH_(3)COOH_((aq))+CH_(3)OH_((aq))` Rate `= k[CH_(3)COOCH_(3)][H_(2)O]` (iv) If the reaction is carried out with the large excess of water, there is no significant change in the concentration of water during hydrolysis, i.e., concentration of water remains almost a constant. (v) Now, we can define `k [H_(2)O]=k'`, Therefore the above rate equation becomes Rate `= k' [CH_(3)COOCH_(3)]` (vi) Thus it follows first order KINETICS. |
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