Hydrogenation of carbon double bonds C=C (i.e. adding a hydrogen on each carbon

Question

Hydrogenation of carbon double bonds C=C (i.e. adding a hydrogen on each carbon atom and thus reducing the double bond into a single bond: H-C-C-H) is a very common process in organic and polymer chemistry. Using the data from the following table, calculate the ?Hreaction when ethylene C2H4 is reduced into ethane according to the reaction below: C2H4(g) + H2(g) --> C2H6(g) Bond Bond enthalpy (kJ/mol) C=C 620 C-C 347 H-H 436 C-H 414 The ?Hreaction is 1.----- kJ/mol

Explanation / Answer

given reaction C2H4(g) + H2(g) --> C2H6(g) given data : Bond enthalpy (kJ/mol) C=C 620 C-C 347 H-H 436 C-H 414 therefore let, dH rxn = dBond energies reactants - products dH rxn = [H-H @463 & C=C @ 620 & 4 C-H @ 414 each] - [C-C @ 347 & 6 C-H @ 414 each] dH rxn = [463+620+(4*414)] - [347+(6*414)] dH rxn = [2,739] - [ 2831] = -91 kJ your answer: -92 kJ (exothermic)

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