Question

For an exothermic reaction, following two steps are involved.
Step 1. $A+B\to I$ (slow)
Step 2. $I\to AB$ (fast)
Which of the following graphs correctly represent this reaction ?

• A.
• B.
• C.
• D.

Answer 1

Answer: (B)

In any reaction mechanism the no. of activated complexes showing maxima of potential energies is the no. of steps in that mechanism and in between these maxima is a valley where lies a more stable intermediate. There is one reaction intermediate lying at valley of two maxima representing two steps. E_a for first step should be higher than second step as first is slow step. These requirements fulfilled by choice (ii) & not choice (i) the choice (iv) is not possible because that is for endothermic reaction $\left(\Delta \text{H}+\text{ve}\right)$ & (ii) is single step equation so not possible.