Question

Energy profile diagram for an exothermic reaction, $A\xrightarrow{1}B\xrightarrow{2}C\xrightarrow{3}D$, is given below.
The rate determining step of the reaction is:

(A) $A \to B$
(B) $B \to C$
(C) $C \to D$
(D) Cannot predict

Answer 1

Hint: For the exothermic reaction, we can say that the step that requires the highest amount of potential energy will be the slowest step of the reaction. The slowest step of the reaction is taken as the rate determining step of the reaction.

Complete answer:
Here, we are given the energy profile diagram of a reaction. We can see that three steps are there in the reaction. We need to find the rate determining step of the reaction.
- We know that the rate determining step of the reaction is the step that determines the rate of the reaction. Generally, the slowest step of the reaction is taken as the rate determining step because it will consume most of the time of the reaction.
- Here, P.E. suggests potential energy of the reaction. It varies as the compounds change. We can see that the potential energy is highest for step-1 and it lowest for step-2. Thus, the energy required for the conversion $A \to B$ will be highest.
- The step in which the highest amount of energy is required will be the slowest step of the reaction. Thus, we can say that step-1 will be the rate determining step of the reaction.
Thus, we can conclude that the rate determining step of the reaction will be $A \to B$.

Therefore, the correct answer is (A).

Note:
The energy required to give the change in the reaction is called activation energy. So, we can say that we need to give energy equal to or more than the activation energy in order to obtain the required change in the reaction.