Explain Steady-State Approximation
Steady-State Approximation
The steady-state approximation is a method used to derive a rate law. The method is based on the assumption that one intermediate in the reaction mechanism is consumed as quickly as it is generated. Its concentration remains the same duraing the reaction.
When a reaction involves one or more intermediates, the concentration of one of the intermediates remains constant at some stage of the reaction. Thus, the system has reached a steady-state. The concentration of one of the intermediates, [Int] , varies with time as shown in Figure. At the start and end of the reaction, [Int] does vary with time.
d[Int]/dT = 0
When a reaction mechanism has several steps with comparable rates, the rate-determining step is not obvious. However, there is an intermediate in some of the steps. The steady-state approximation implies that select an intermediate in the reaction mechanism, and calculate its concentration by assuming that it is consumed as quickly as it is generated.
Example-
A ---K1→ B
B ---K2→ Product
Then-
Rate of production of B = K1[A]
Rate of consumption of B = K2[B]
Accoirding to steady-state approximation, the rate of production of an intermediate(B) is equal to the rate of its consumption. Thus, we have-
K1[A] = K2[B]
