Methanol burns completely in oxygen.
2CH3OH+3O2→2CO2+4H2O \mathrm{2CH_{3}OH + 3O_{2} \rightarrow 2CO_{2} + 4H_{2}O} 2CH3OH+3O2→2CO2+4H2OA methanol molecule contains three C−H\mathrm{C{-}H}C−H bonds, one C−O\mathrm{C{-}O}C−O bond and one O−H\mathrm{O{-}H}O−H bond. Carbon dioxide is O=C=O\mathrm{O{=}C{=}O}O=C=O and water is H−O−H\mathrm{H{-}O{-}H}H−O−H.
| Bond | C−H\mathrm{C{-}H}C−H | C−O\mathrm{C{-}O}C−O | O−H\mathrm{O{-}H}O−H | O=O\mathrm{O{=}O}O=O | C=O\mathrm{C{=}O}C=O |
|---|---|---|---|---|---|
| Bond energy (kJ/mol\mathrm{kJ/mol}kJ/mol) | 413 | 358 | 464 | 498 | 805 |
What is the energy change when one mole of methanol burns?
−1316 kJ/mol-1316\,\mathrm{kJ/mol}−1316kJ/mol
−658 kJ/mol-658\,\mathrm{kJ/mol}−658kJ/mol
−1122 kJ/mol-1122\,\mathrm{kJ/mol}−1122kJ/mol
+658 kJ/mol+658\,\mathrm{kJ/mol}+658kJ/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.