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Using the bond enthalpies given below, determine the enthalpy change for the hydrogenation reaction shown: H–H bond energy = 431.37 kJ mol⁻¹ C–C bond energy = 606.10 kJ mol⁻¹ C–H bond energy = 336.49 kJ mol⁻¹ C–H bond energy = 410.50 kJ mol⁻¹ C=C + H–H → H–C–C–H What is the enthalpy change for this reaction?

1. -243.6 kJ mol⁻¹
2. -120.0 kJ mol⁻¹
3. 553.0 kJ mol⁻¹
4. 1523.6 kJ mol⁻¹

Correct answer: -243.6 kJ mol⁻¹

Solution

The enthalpy change for the reaction is calculated by subtracting the total bond energies of the products from the total bond energies of the reactants. In this case, breaking the C=C and H–H bonds requires energy, while forming C–H bonds releases energy, resulting in a net release of energy of -243.6 kJ mol⁻¹.

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