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Electron Sharing Reactions · Paper 2 — Free Chemistry HL Practice Questions

1MasterySAQ-SCovalent bonds and electron sharing5 marksPaper 2~8 min
Ethene (C2H4\text{C}_2\text{H}_4) is an unsaturated hydrocarbon used in the manufacture of polymers. Each carbon atom in ethene forms three sigma bonds and one pi bond.
(a)
State the number of sigma (σ\sigma) bonds and pi (π\pi) bonds present in the carbon–carbon double bond of ethene. [1 mark]
(b)
Use the bond enthalpy data below to calculate the enthalpy change, in kJ mol−1\text{kJ mol}^{-1}, for the hydrogenation of ethene: C2H4(g)+H2(g)→C2H6(g)\text{C}_2\text{H}_4(\text{g}) + \text{H}_2(\text{g}) \rightarrow \text{C}_2\text{H}_6(\text{g}) | Bond enthalpy / kJ mol−1\text{kJ mol}^{-1} | C=C — +612+612 C–C — +348+348 H–H — +436+436 [2 marks]
(c)
Explain, in terms of orbital overlap, why the pi bond in the C=C double bond is weaker than the sigma bond. [2 marks]
diagram

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