Carbon dioxide reacts with hydrogen to make methane and water.
CO2+4H2→CH4+2H2O \mathrm{CO_2 + 4H_2 \rightarrow CH_4 + 2H_2O} CO2+4H2→CH4+2H2OThe energy change for the equation as written is -150 kJ/mol.
A carbon dioxide molecule has the displayed formula O=C=O\mathrm{O{=}C{=}O}O=C=O. Each hydrogen molecule contains one H−H\mathrm{H{-}H}H−H bond, each methane molecule contains four C−H\mathrm{C{-}H}C−H bonds, and each water molecule contains two O−H\mathrm{O{-}H}O−H bonds.
| Bond | H−H\mathrm{H{-}H}H−H | C−H\mathrm{C{-}H}C−H | O−H\mathrm{O{-}H}O−H |
|---|---|---|---|
| Bond energy (kJ/mol\mathrm{kJ/mol}kJ/mol) | 436 | 413 | 463 |
Calculate the bond energy of the C=O\mathrm{C{=}O}C=O bond. Show your working.
Suggest why the bond energy calculated in part (a) is only an estimate.
106 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.