Ethene reacts with hydrogen to make ethane.
C2H4+H2→C2H6 \mathrm{C_{2}H_{4} + H_{2} \rightarrow C_{2}H_{6}} C2H4+H2→C2H6Ethene contains one C=C\mathrm{C{=}C}C=C bond and four C−H\mathrm{C{-}H}C−H bonds. Ethane contains one C−C\mathrm{C{-}C}C−C bond and six C−H\mathrm{C{-}H}C−H bonds.
| Bond | C=C\mathrm{C{=}C}C=C | C−C\mathrm{C{-}C}C−C | C−H\mathrm{C{-}H}C−H | H−H\mathrm{H{-}H}H−H |
|---|---|---|---|---|
| Bond energy (kJ/mol\mathrm{kJ/mol}kJ/mol) | 612 | 347 | 413 | 436 |
What is the energy change for the reaction?
+125 kJ/mol+125\,\mathrm{kJ/mol}+125kJ/mol
+288 kJ/mol+288\,\mathrm{kJ/mol}+288kJ/mol
−125 kJ/mol-125\,\mathrm{kJ/mol}−125kJ/mol
−43 kJ/mol-43\,\mathrm{kJ/mol}−43kJ/mol
51 exam-style questions on OCR GCSE Chemistry 3.2 Energetics, covering 3.2.1 Exothermic and endothermic reactions and reaction profiles and 3.2.2 Calculating energy change from bond energies. Each one has a worked solution and a mark scheme showing where the marks go.