Question

The depletion of ozone involves the following steps:Step 1: O3 --> O2 + O (fast)Step 2: O3 + O ----> 2O2 (slow)The predicted order of the reaction will be?​

Answer 1

Topic :- Chemical kinetics

Concept

• Order if a reaction is the sum of power of reactants involved in rate law expression.

For example:- If the rate law expression is R = K [A]²[B]

The order is 2 + 1 = 3

• Order has nothing to do with stiochiometric coefficients

• For an elementary reaction A + B $\rightarrow$

Rate = k [A] [B] ( Same as that of stiochiometric coefficients)

• Order of a complex reaction is decided by the slowest step. .Further, species occurring in the intermediate steps are not included in rate law expression.

Solutions

Given,

The depletion of $O_3$ occurs in two steps

Step 1 :- $O_3$ $\rightarrow$ $O_2$ + O

Step 2 :- $O_3$ + O $\rightarrow$ $2O_2$ ( R.D.S.)

Since, it is R.D.S and also an elementary reaction , Rate if reaction will be

k [ $O_3$ ] [O] ( O is an intermediate species, we should eliminate it )

Now, Assuming the reactions to be equilibrium, we can further substitute for the value of [0].

Refer to the attachment for further solution

The order of the reaction is 4/3.