Question

Which of the following statements about an elementary process or step is/are correct? 1) Intermediates in a reaction cannot be involved in the rate determining step ii) In the rate equation for the forward reaction of an elementary step, the overall reaction order is equal to the number of reactant molecules in the step iii) To be the rate determining step in a mechanism, an elementary step must be exothermic O A. ii and ill only B. i and iii only C. i only O OD. ii only O E. i only

Answer 1

1. Elementry reactions are single step reactions . No intermediate is formed in between.

but it is not compulsory that elementry step is rate determing step..

so in general intermediate can be involved in rate determing step. depending upon whether this step is slow or fast.

so 1st statment  is not correct.

2. In elementary reactions order of the reaction is equal to the number of molecules of the reactant (not the no of diffrent type of molecules reacting) involved which is also equal to the sum of stichiometry of the reactants.

generally in elementry reactions this no. does not exceed 3. because more than 3 molecules can not collide simultaneously so  effectively to form a product.

so 2nd statement is correct.

3. It is not compulsory for elementry reactions to be exothermic.

so 3rd statement is not correct.

So the correct ans. is option D ii only.

hope you are satisfied with my ans.