Define the term mean bond enthalpy.
Tetrafluorohydrazine (N2F4\text{N}_2\text{F}_4N2F4) is a highly reactive gas that can undergo a reduction reaction with hydrogen (H2\text{H}_2H2) in the gas phase according to the equation: N2F4(g)+2H2(g)→N2(g)+4HF(g)\text{N}_2\text{F}_4(g) + 2\text{H}_2(g) \rightarrow \text{N}_2(g) + 4\text{HF}(g)N2F4(g)+2H2(g)→N2(g)+4HF(g) The enthalpy change for this reaction is ΔH=−1049 kJ mol−1\Delta H = -1049\text{ kJ mol}^{-1}ΔH=−1049 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−F\text{N}-\text{F}N−F | 278 |
| H−H\text{H}-\text{H}H−H | 436 |
| N≡N\text{N}\equiv\text{N}N≡N | 945 |
| H−F\text{H}-\text{F}H−F | 562 |
Use the data in Table 1 to calculate a value for the N−N\text{N}-\text{N}N−N bond enthalpy in tetrafluorohydrazine.