First slide

Enthalpy of Atomisation and bond dissociation

Question

What is the heat of hydrogenation of ethene if the bond energies of C- C, C = C, H-H, and C-H are 350, 600, 440 and 410 kJ/mole respectively?

Easy

A

-130 kJ/mol
B

-260 kJ/mol
C

-400 kJ/mol
D

-450 kJ/mol

Solution

$ΔH = Σ$ Bond energy of reactants
$- Σ$ Bond energy of products
$\begin{array}{l} ΔH \\ = [4 {ΔH}_{C - H} + {ΔH}_{C = C} + {ΔH}_{H - H}] \\ - [{ΔH}_{C - C} + 6 {ΔH}_{C - H}] \\ = [4 \times 410 + 600 + 440] \\ - [350 + 2460] \\ = 2680 - 2810 = - 130 {kJmol}^{- 1} \end{array}$

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