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CONSECUTIVE OR SEQUENTIAL REACTION:


A chemical reaction in which the product form is further decomposed into another product such kind reaction of reaction is known as sequential reaction.
If rate constant of reaction is K1 and K2 then the rate of reaction is for the reaction

For the determination of concentration of A after time t, integrating equation (1)
For the determination of concentration of B after time t,
Net rate of formation of [B]
Multiply eK2t to both side and integrating
For the determination of concentration of [C] after time t,
Since by law of mass balance [A]0=[A]t +[B]t+[C]t
Graphical representation of concentration of A B and C after time t that is [A]t , [B]t and [C]t respectively.
Case (1):  K1 >>>K2
Concentration of [B]t: when K1>>>K2 in this case we can observed that reaction first (A to B) occurs first and gives nearly to completion before reaction (B to C) take place. Thus nearly all the (A) is converted to the intermediate (B) before any appreciable conversion of (B to C), thus
Concentration of [C]t:
Graphical representation:
In general concentration of [A] decreases exponentially, and the concentration of [B] Initially increases up to a maximum and then decrease therefore and concentration of [C] increases steadily until it  reaches its final value [A]0, when all A has changed into [C]
Case (2): K2 >>>K1
Concentration of [B]t:
Since K2>>>K1 then second term in parenthesis rapidly approaches zero while the first term is still near unity consequently concentration of [B] approaches to K1/K2 [A] and decay more slowly according to 
Since k1/K2 is very small, the maximum concentration of [B] is much less than [A]0

Concentration of [C]t:
Graphical representation:
Calculation of Maximum concentration of [B] and Maximum time:
Examples of consecutive reactions:
Illustrative Examples:

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