Calculate Δ S universe for following chemical reaction at 300 K C (graphite) +2H₂(g) ⟶ CH₄(g) ; The standard enthalpy of formation of CH₄ is –75 kJ mol⁻¹. The standard entropies of C (graphite), H₂(

Question

Calculate Δ S universe ​ for following chemical reaction at 300 K C (graphite) +2H₂(g) ⟶ CH₄(g) ; The standard enthalpy of formation of CH₄ is –75 kJ mol⁻¹. The standard entropies of C (graphite), H₂(g), and CH₄(g) are 5 J/K·mol, 130 J/K·mol, and 186 J/K·mol, respectively.

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Explanation: Calculate Δ S u ni v erse ​ for a chemical reaction at 300 K. Concept: Calculation of entropy of a chemical reaction. Solution: Calculate Δ S sys t e m ​ Δ S sys ​ = Σ S P ro d u c t s ◦ ​ − Σ S re a c t an t s ◦ ​ × \displaylines Δ S sys ​ = S ◦ ​ ( C H 4 ​ ) − [ S ◦ ​ ( C ) + 2 × S ◦ ​ ( H 2 ​ ) ] Δ S sys ​ = 186 − [ 5 + 2 ( 130 ) ] = 186 − 265 = − 79 K J ​ Calculate Δ S s u rro u n d in g s ​ : Δ S s u rr ​ = T − Δ H sys ​ ​ = 300 K − ( − 75000 J ) ​ = + 250 K J ​ Calculate Δ S u ni v rse ​ Δ S u ni v rse ​ = − 79 + 250 = 171 k J ​

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JEE Advanced (2028)