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neha kondekar Grade:
`        in psuedo first order reacn of acid hydrolysis of ester does rate depend on ph?`
6 years ago

## Answers : (1)

SAGAR SINGH - IIT DELHI
879 Points
```										Dear neha,
This is a second-order reaction in which one of the reactants is present  in such great amounts that its effect is not seen. For example, the  hydrolysis of an ester in water. If the water is present in great  amounts, any change will be too small, relatively, to be noticed. The  reaction then appears dependent on concentration of ester alone. To see  the dependence on water, you'd have to dissolve the ester in acetone  with a few % water.
For example we have a reaction   A + B ==> Product   the rate of reaction is .....   Rate= dP/dt .... which is also the same as ....  Rate = K.[A].[B]   The total order of reaction will equal to the sum of the orders of the  reactants A + B  = 1+1 = 2 ... so the above reaction is a second order  reaction.   Now If we converted one of those reactants to be in excess concentration  in the system, then we can get a pseudo first order reaction  example ConcA = 0.1M  excess ConcB = 1M   after the reaction [A] = 0 and [B] = 0.99M  so reactant B wont contribute to the total order as it is in excess and  viewed as a constant, this is known as pseudo first order.  so the new rate = K'.[A]          and the total order is = to the sum of the orders which is = to 1,  as [A] is the only reactant contributing to the rate.  K' = K.[B]   but member even though [B] is assumed as a constant any large changes in [B] will effect K' and therefore effect the rate.

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Sagar Singh
B.Tech, IIT Delhi

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6 years ago
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