Describe isolation method in determination of rate law and order of reaction.
1) In the isolation method, the concentrations of all the reactants except one are made to remain constant throughout the course of the reaction by taking them in large excess. The dependence of rate on the concentration of the isolated species is experimentally determined.
2) The experiment is repeated by isolating one of the reactants each time and determining the rate law with respect to the isolated species.
3) Consider the reaction, aA + bB → cC + dD
The rate law has the form,
Rate = k[A]x[B]y
4) In one of the experiment, A is isolated by making the initial concentration of B (i.e., [B]0) to remain constant throughout the course of the reaction (by taking it in large excess).
Hence, the rate law is written as
rate = k[A]x `[B]_0^y = k'[A]x (where, k' = `k[B]_0^y` )`
The dependence of rate on [A] that is ‘x’ is found out.
5) In another experiment, B is isolated by keeping initial concentration of A (i.e., [A]0) constant throughout the course of the reaction (i.e., by taking it in large excess). The rate law then becomes, Rate = `k [A]_0^x[B]^y = K" [B]^y` (where k" = `k[A]_0^x`).
The dependence of rate on B that is y is found out
Thus, by knowing the values of x and y, the order of the reaction (x + y) and the rate
law can be determined.
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