If the enthalpy of combustion of C H 3 OH ( l ) is Δ C H , then calculate the value of ∣Δ CH ∣ × 134 1 . Given: Resonance energy of C O 2 = –140 kJ mol⁻¹ Δ v a p or i s a t i o n H ( C H 3

Question

If the enthalpy of combustion of C H 3 ​ OH ( l ) is Δ C ​ H , then calculate the value of ∣Δ CH ∣ × 134 1 ​ . Given: Resonance energy of C O 2 ​ = –140 kJ mol⁻¹ Δ v ​ a p or i s a t i o n H ( C H 3 ​ OH , l ) = 35 kJ mol⁻¹ Δ v ​ a p or i s a t i o n H ( H 2 ​ O , l ) = 40 kJ mol⁻¹ Bond: C–H, C–O, O=O, C=O, O–H Bond Energy: 410, 355, 490, 710, 460 (kJ mol⁻¹)

TestHub · Accepted Answer

​ C H 3 ​ OH + 2 3 ​ O 2 ​ ( g ) → C O 2 ​ ( g ) + 2 H 2 ​ O ( s ) Δ C ​ H = { Δ H v a p ⋅ ( C H 3 ​ OH ) ​ + 3 BE C − H ​ + BE O − H ​ + BE C − O ​ + 2 3 ​ BE O = O ​ } − { 2 ( Δ H v a p . ( H 2 ​ O ) ​ ) + 2 BE C = O ​ + 4 BE O − H ​ } = { 35 + 3 ( 410 ) + 355 + 460 + 2 3 ​ × 490 } − { 2 × 40 + 2 × 710 + 4 ( 460 ) } = 2815 − 3480 = − 665 kJ/mol 134 Δ C ​ H ​ = 134 − 665 ​ ≈ − 4.96 kJ/mol ≈ − 5 kJ/mol ​

Chemistry - Thermochemistry Question with Solution | TestHub

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