NEET 2021 · ChemistryPrevious Year Question

For a reaction $A B$ , the enthalpy of reaction is $- 4.2 k J m o l^{- 1}$ and the enthalpy of activation is $9.6 k J m o l^{- 1}$ . The correct potential energy profile for the reaction is shown in which option?

Answer: (D) PE profile: A at higher energy, curve rises over a small barrier, B settles at a level lower than A (exothermic, $Δ H$ negative).. \textbf{Answer:} (D) \textbf{Solution:} The enthalpy of reaction $Δ H = - 4.2 k J m o l^{- 1}$ is negative, so the reaction is exothermic and the products (B) lie at lower potential energy than the reactants (A).

NEET 2021 Chemistry question — For a reaction A -> B, the enthalpy of reaction is -4.2 kJ,mol-1 and the enthalpy of…

A.PE profile: A at low energy, curve rises to a high peak, B comes down to a level higher than A (endothermic, large barrier).
B.PE profile: A at low energy, curve rises over a barrier, B settles at a level higher than A (endothermic).
C.PE profile: A and B at roughly the same energy level with a barrier in between (approximately thermoneutral).
D.PE profile: A at higher energy, curve rises over a small barrier, B settles at a level lower than A (exothermic, $Δ H$ negative).✓

Correct Answer

(D) PE profile: A at higher energy, curve rises over a small barrier, B settles at a level lower than A (exothermic, $Δ H$ negative).

Solution & Explanation

\textbf{Answer:} (D) \textbf{Solution:} The enthalpy of reaction $Δ H = - 4.2 k J m o l^{- 1}$ is negative, so the reaction is exothermic and the products (B) lie at lower potential energy than the reactants (A). The curve rises by the activation enthalpy ( $9.6 k J m o l^{- 1}$ ) to a barrier, then drops to B below A. Only profile (D) shows B below A. Mapped: source lowercase answer 'd' → option D.

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For a reaction A​B, the enthalpy of reaction is −4.2 kJmol−1 and the enthalpy of activation is 9.6 kJmol−1. The correct potential energy profile for the reaction is shown in which option?

Solution & Explanation

More NEET PYQ solutions

For a reaction $A B$ , the enthalpy of reaction is $- 4.2 k J m o l^{- 1}$ and the enthalpy of activation is $9.6 k J m o l^{- 1}$ . The correct potential energy profile for the reaction is shown in which option?