Ethene burns in oxygen to make carbon dioxide and water.
C2H4+3O2→2CO2+2H2O \mathrm{C_2H_4 + 3O_2 \rightarrow 2CO_2 + 2H_2O} C2H4+3O2→2CO2+2H2OThe bonds present in one molecule are shown in the table.
| Substance | Bonds in one molecule |
|---|---|
| C2H4\mathrm{C_2H_4}C2H4 | four C−H\mathrm{C{-}H}C−H bonds and one C=C\mathrm{C{=}C}C=C bond |
| O2\mathrm{O_2}O2 | one O=O\mathrm{O{=}O}O=O bond |
| CO2\mathrm{CO_2}CO2 | two C=O\mathrm{C{=}O}C=O bonds |
| H2O\mathrm{H_2O}H2O | two O−H\mathrm{O{-}H}O−H bonds |
| Bond | C−H\mathrm{C{-}H}C−H | C=C\mathrm{C{=}C}C=C | 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 | 612 | 498 | 805 | 463 |
Calculate the energy change for the reaction.
Show your working.
Explain what your answer to part (a) shows about this reaction, and predict how the temperature of the surroundings changes.
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.