NEET 2025 · ChemistryPrevious Year Question
$\ce{C(s) + 2H2(g) -> CH4(g)}$; $\Delta H = -74.8\ kJ\,mol^{-1}$. Which of the following diagrams gives an accurate representation of the above reaction? [R $\rightarrow$ reactants; P $\rightarrow$ products]
- A.Energy-level diagram: reactants (R) and products (P) at nearly the same level with P only marginally below R.
- B.Energy-level diagram: products (P) at higher energy than reactants (R), endothermic.
- C.Energy-level diagram: reactants (R) at higher energy, an activation hump, and products (P) at lower energy than R — exothermic.✓
- D.Energy-level diagram: products (P) at a higher peak than reactants (R).
Correct Answer
(C) Energy-level diagram: reactants (R) at higher energy, an activation hump, and products (P) at lower energy than R — exothermic.
Solution & Explanation
\textbf{Answer:} (C) \textbf{Solution:} $\Delta H = -74.8\ kJ\,mol^{-1} < 0$, so the reaction is exothermic: energy is released and the products lie at lower energy than the reactants. Only diagram (C) shows P below R (reactants higher, products lower, with the energy released equal to $74.8\ kJ\,mol^{-1}$). Mapped: source lowercase answer 'c' → option C.
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