Carbon dioxide reacts with hydrogen to make methane and water vapour.
CO2+4H2→CH4+2H2O \mathrm{CO_{2} + 4H_{2} \rightarrow CH_{4} + 2H_{2}O} CO2+4H2→CH4+2H2OThe table shows some bond energies.
| Bond | Bond energy (kJ/mol) |
|---|---|
| C=O | 805 |
| H-H | 436 |
| C-H | 413 |
| O-H | 463 |
During the reaction, the bonds in carbon dioxide and hydrogen are broken. Explain the energy transfer involved.
Calculate the energy change for the reaction.
The measured energy change for the reaction is -165 kJ/mol.
Compare this value with your answer to (b). Explain why the values may differ and whether they lead to the same prediction for the reaction profile.
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.