Using the mean bond enthalpies below, estimate ΔrH for the gas-phase hydrogenation of ethene: CH₂=CH₂(g) + H₂(g) → CH₃–CH₃(g) C=C: 614 kJ mol⁻¹; C–C: 348 kJ mol⁻¹; C–H: 413 kJ mol⁻¹; H–H: 436 kJ mol⁻¹

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