JEE Main 2026 Jan 24 Shift 1, Chemistry Q2: Basic Concepts of Thermodynamic

JEE Main2026Jan 24, Shift 1Chemistry

$A \to D$ is an endothermic reaction occurring in three steps (elementary).

(i) $A \to B$ $Δ H_{i} = + v e$

(ii) $B \to C$ $Δ H_{ii} = - v e$

(iii) $C \to D$ $Δ H_{iii} = - v e$

Which of the following graphs between potential energy (y-axis) vs reaction coordinate (x-axis) correctly represents the reaction profile of $A \to D$ ?

Solution

From the step enthalpies:

$A \to B$ : $Δ H = + v e \Rightarrow E_{B} > E_{A}$

$B \to C$ : $Δ H = - v e \Rightarrow E_{C} < E_{B}$

$C \to D$ : $Δ H = - v e \Rightarrow E_{D} < E_{C}$

Overall $A \to D$ is endothermic, so $E_{D} > E_{A}$ .

Combining: $E_{A} < E_{D} < E_{C} < E_{B}$ .

The correct profile rises steeply from A to the highest intermediate B, descends to a lower intermediate C, then descends further to D, which still lies above A. This matches graph (3).

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JEE Main 2026 Jan 24 Shift 1, Chemistry Q2: Basic Concepts of Thermodynamic

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