Define the term mean bond enthalpy.
Hydrazine (N2H4\text{N}_2\text{H}_4N2H4) is used as a rocket propellant that is oxidised by hydrogen peroxide (H2O2\text{H}_2\text{O}_2H2O2) in the gas phase according to the equation:
N2H4(g)+2H2O2(g)→N2(g)+4H2O(g) \text{N}_2\text{H}_4(g) + 2\text{H}_2\text{O}_2(g) \rightarrow \text{N}_2(g) + 4\text{H}_2\text{O}(g) N2H4(g)+2H2O2(g)→N2(g)+4H2O(g)The enthalpy change for this reaction is ΔH=−795 kJ mol−1\Delta H = -795\text{ kJ mol}^{-1}ΔH=−795 kJ mol−1.
Table 1 shows some mean bond enthalpy values:
| Bond | Mean bond enthalpy / kJ mol−1\text{kJ mol}^{-1}kJ mol−1 |
|---|---|
| N−H\text{N}-\text{H}N−H | 391 |
| O−O\text{O}-\text{O}O−O | 144 |
| N≡N\text{N}\equiv\text{N}N≡N | 945 |
| O−H\text{O}-\text{H}O−H | 463 |
Use the data in Table 1 to calculate a value for the N−N\text{N}-\text{N}N−N bond enthalpy in hydrazine.