Hydrazine, N2H4\mathrm{N_{2}H_{4}}N2H4, burns in oxygen.
N2H4+O2→N2+2H2O \mathrm{N_{2}H_{4} + O_{2} \rightarrow N_{2} + 2H_{2}O} N2H4+O2→N2+2H2OEach hydrazine molecule contains one N−N\mathrm{N{-}N}N−N bond and four N−H\mathrm{N{-}H}N−H bonds. Water is H−O−H\mathrm{H{-}O{-}H}H−O−H.
| Bond | N−H\mathrm{N{-}H}N−H | N−N\mathrm{N{-}N}N−N | O=O\mathrm{O{=}O}O=O | N≡N\mathrm{N{\equiv}N}N≡N | O−H\mathrm{O{-}H}O−H |
|---|---|---|---|---|---|
| Bond energy (kJ/mol\mathrm{kJ/mol}kJ/mol) | 391 | 158 | 498 | 945 | 464 |
What is the energy change for the reaction?
+347 kJ/mol+347\,\mathrm{kJ/mol}+347kJ/mol
−739 kJ/mol-739\,\mathrm{kJ/mol}−739kJ/mol
−581 kJ/mol-581\,\mathrm{kJ/mol}−581kJ/mol
+581 kJ/mol+581\,\mathrm{kJ/mol}+581kJ/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.