Question

Given a reaction mechanism that has an overall reaction of 2O3 mc010-1.jpg 3O2 and a rate of k[O3][O], which is the correct rate-determining step?
O3 + 2O mc010-2.jpg 3O2
O2 + O mc010-3.jpg O3
O3 mc010-4.jpg O2 + O
O3 + O mc010-5.jpg 2O2

Answer 1

Answer: The correct answer is $O_3+O\rightleftharpoons 2O_2$

Explanation: Rate of the reaction is studied on the basis of Law of Mass Action. Rate law is the expression which expresses the rate of the reaction in the terms of molar concentrations of the reactants with each term raised to the power of their stoichiometric ratios.

For the equation:

$aA+bB\rightarrows cC+dD$

Rate is written by the equation:

$Rate=k[A]^a[B]^b$

Rate is always determined by the slowest step and it is known as rate-determining step.

For the total reaction,

$2O_3\rightarrow 3O_2$

The rate given is $k[O_3][O]$

This expression is given by the equation in which reactants are $O_3\text{ and }O$ and the stoichiometry of the reactants is 1. Hence, the equation from which the rate is written is $O_3+O\rightleftharpoons 2O_2$

Answer 2

The overall reaction and rate equation tell us that O₃ and O are the reactants. Only the first and last equations contain these two as reactants; however, the first equation is not balanced. Therefore, the answer is:
O₃ + O → 2O₂