The average S - F bond energy in kJ mol ^ - 1 of SF _ 6 is _....

${SF}_{6}\left(g\right) \to S\left(g\right) + 6F\left(g\right)$

If $\in$- bond enthalpy

${\Delta}_{r}H = 6 \times {ϵ}_{S - F}$

$= {\Delta}_{f}H\left(S, g\right) + 6 \times {\Delta}_{f}H\left(F, g\right) - {\Delta}_{f}H\left({SF}_{6}, g\right)$

$= 275 + 6 \times 80 - \left(- 1100\right)$

$= 1855kJ$

${ϵ}_{S - F} = \dfrac{1855}{6} = 309 . 16kJ{mol}^{- 1}$