Given the data below : Δ H c 0 o mb ( C H 4 , g ) = − 900 k J / m o l e Δ H c 0 o mb ( C , g r a p hi t e ) = − 400 k J / m o l Δ H c 0 o mb ( H 2 , g ) = − 300 k J / m o l Δ H a 0 t o mi

Question

Given the data below : Δ H c 0 ​ o mb ( C H 4 ​ , g ) = − 900 k J / m o l e Δ H c 0 ​ o mb ( C , g r a p hi t e ) = − 400 k J / m o l Δ H c 0 ​ o mb ( H 2 ​ , g ) = − 300 k J / m o l Δ H a 0 ​ t o mi s a t i o n ( C , g r a p hi t e ) = 700 k J / m o l Δ H f 0 ​ ( H , g ) = 220 k J / m o l What should be the bond enthalpy of the C–H bond in kJ/mole?

TestHub · Accepted Answer

C ( s ) + 2 H 2 ​ ( g ) ⟶ CH 4 ​ ( g ) Δ H ∘ f ​ ( CH 4 ​ ) = Δ H req ​ Δ H reactionn ​ = Δ H sub ​ + 2 ( ε H − H ​ ) − 4 ( ε C − H ​ ) Given: 2 1 ​ H 2 ​ ( g ) ⟶ H ( g ) 220 kJ / Mol ∴ 2 1 ​ ( B.E. H − H ​ ) = 220 ( BE H − H ​ ) = 440 kJ / mol ⟶ ε H − H ​ Δ H reaction ​ = Δ H ∘ C ( graphite ) ​ + 2Δ H ∘ C ​ − 4 ( ε C − H ​ ) = − 400 × 2 ( − 300 ) − ( − 900 ) = − 100 kJ / mol For equation (1) Δ H sub ​ + 2 ( ε H − H ​ ) − 4 ( ε C − H ​ ) = − 100 700 + 2 ( 440 ) − 4 ( ε C − H ​ ) = − 100 ( ε C − H ​ ) = 420 kJ / mol

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