$A \rightarrow D$ is an endothermic reaction occurring in three elementary steps:
(i) $A \rightarrow B \quad \Delta H_i = +\text{ve}$
(ii) $B \rightarrow C \quad \Delta H_{ii} = -\text{ve}$
(iii) $C \rightarrow D \quad \Delta H_{iii} = -\text{ve}$
Which of the following graphs between potential energy (y-axis) versus reaction coordinate (x-axis) correctly represents the reaction profile of $A \rightarrow D$?

Question

Consider the following compounds. Arrange these compounds in a n increasing order of reactivity with nitrating mixture. The correct order is :

Answer 1

To determine which graph correctly represents the reaction profile of the endothermic reaction $A \rightarrow D$ that occurs in three steps, let's analyze the information given:

The first step $A \rightarrow B$ is endothermic, indicated by $\Delta H_i = +\text{ve}$. This implies that there is an increase in potential energy as the reaction progresses from $A$ to $B$.
The second step $B \rightarrow C$ is exothermic, indicated by $\Delta H_{ii} = -\text{ve}$. This implies that the potential energy decreases from $B$ to $C$.
The third step $C \rightarrow D$ is also exothermic, denoted by $\Delta H_{iii} = -\text{ve}$, indicating another decrease in potential energy from $C$ to $D$.

Since the overall reaction $A \rightarrow D$ is endothermic, the final energy level of $D$ must be higher than that of $A$. When all steps are considered together, the energy profile should start at $A$, increase to a peak at $B$, decrease through $C$, and finish at $D$ such that $D$'s energy is still higher than $A$.

Analyzing the options given:

Option 1 shows an incorrect order of potential energies implying incorrect reaction profile.
This option correctly shows the energy level of $B$ as higher than $A$, begins with an endothermic phase from $A$ to $B$, followed by two exothermic transitions decreasing energy to $C$ and then to $D$, with energy at $D$ still higher than $A$. Hence, this graph accurately depicts the endothermic nature of the overall reaction.
Options 3 and 4 either have the wrong energy transitions or incorrect final energy level relative to $A$.

Therefore, the correct graph representing the reaction profile for $A \rightarrow D$ is option 2.

Answer 2

To determine which graph correctly represents the reaction profile of the endothermic reaction $A \rightarrow D$ that occurs in three steps, let's analyze the information given:

The first step $A \rightarrow B$ is endothermic, indicated by $\Delta H_i = +\text{ve}$. This implies that there is an increase in potential energy as the reaction progresses from $A$ to $B$.
The second step $B \rightarrow C$ is exothermic, indicated by $\Delta H_{ii} = -\text{ve}$. This implies that the potential energy decreases from $B$ to $C$.
The third step $C \rightarrow D$ is also exothermic, denoted by $\Delta H_{iii} = -\text{ve}$, indicating another decrease in potential energy from $C$ to $D$.

Since the overall reaction $A \rightarrow D$ is endothermic, the final energy level of $D$ must be higher than that of $A$. When all steps are considered together, the energy profile should start at $A$, increase to a peak at $B$, decrease through $C$, and finish at $D$ such that $D$'s energy is still higher than $A$.

Analyzing the options given:

Option 1 shows an incorrect order of potential energies implying incorrect reaction profile.
This option correctly shows the energy level of $B$ as higher than $A$, begins with an endothermic phase from $A$ to $B$, followed by two exothermic transitions decreasing energy to $C$ and then to $D$, with energy at $D$ still higher than $A$. Hence, this graph accurately depicts the endothermic nature of the overall reaction.
Options 3 and 4 either have the wrong energy transitions or incorrect final energy level relative to $A$.

Therefore, the correct graph representing the reaction profile for $A \rightarrow D$ is option 2.

Show Hint

The Correct Option is B

Solution and Explanation

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