Methane burns completely in oxygen.
CH4+2O2→CO2+2H2O \mathrm{CH_{4} + 2O_{2} \rightarrow CO_{2} + 2H_{2}O} CH4+2O2→CO2+2H2OA methane molecule has four C−H\mathrm{C{-}H}C−H bonds. 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 | O=O\mathrm{O{=}O}O=O | C=O\mathrm{C{=}O}C=O | O−H\mathrm{O{-}H}O−H |
|---|---|---|---|---|
| Bond energy (kJ/mol\mathrm{kJ/mol}kJ/mol) | 413 | 498 | 805 | 464 |
What is the energy change for the reaction?
−818 kJ/mol-818\,\mathrm{kJ/mol}−818kJ/mol
−1316 kJ/mol-1316\,\mathrm{kJ/mol}−1316kJ/mol
+110 kJ/mol+110\,\mathrm{kJ/mol}+110kJ/mol
+818 kJ/mol+818\,\mathrm{kJ/mol}+818kJ/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.