Bond energies are used to analyse two reactions.
Reaction 1 is:
CH4+2O2→CO2+2H2O \mathrm{CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O} CH4+2O2→CO2+2H2OThe energy change for reaction 1 is -814 kJ/mol.
Reaction 2 is:
2H2+O2→2H2O \mathrm{2H_2 + O_2 \rightarrow 2H_2O} 2H2+O2→2H2OThe table shows some bond energies.
| Bond | C−H\mathrm{C-H}C−H | C=O\mathrm{C=O}C=O | O−H\mathrm{O-H}O−H | H−H\mathrm{H-H}H−H |
|---|---|---|---|---|
| Bond energy (kJ/mol\mathrm{kJ/mol}kJ/mol) | 413 | 805 | 463 | 436 |
Calculate the bond energy of the O=O\mathrm{O=O}O=O bond.
Use your answer to part (a) to calculate the energy change for reaction 2 and state whether reaction 2 is exothermic or endothermic.
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.