Use the bond enthalpies given to estimate the heat released when ethene,CH₂=CH₂,reacts with hydrogen to give CH₃CH₃.Bond enthalpies (kJ.mol^-¹): C-H,412; C-C,348; C=C,612; C-Br,276; H-H,436.

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The heat released is equal to the difference between the bond enthalpies of the reactants and the products. The bond enthalpies of the reactants are:C-H: 412 kJ/mol x 4 = 1648 kJ/molC-C: 348 kJ/molC=C: 612 kJ/molH-H: 436 kJ/mol x 2 = 872 kJ/molThe bond enthalpies of the products are:C-H: 412 kJ/mol x 6 = 2472 kJ/molC-C: 348 kJ/molThe heat released is therefore:2472 kJ/mol + 348 kJ/mol - 1648 kJ/mol - 348 kJ/mol - 612 kJ/mol - 872 kJ/mol = 124 kJ/mol

Use the Bond Enthalpies Given to Estimate the Heat Released