For the reaction H _ 2 F _ 2 (g) → H _ 2 (g) + F _ 2 (g) Δ U = - 59...

For the reaction ${H}_{2}{F}_{2}\left(g\right) \to {H}_{2}\left(g\right) + {F}_{2}\left(g\right)$

$\Delta H = \Delta U + \left({\Delta n}_{g}\right)RT$

Given $\Delta U = - 59 . 6kJ{mol}^{- 1}$

${\Delta n}_{g} = 2 - 1$

$= - 59 . 6 + 1 \times \dfrac{8 . 314}{1000} \times 300$

$= - 57 . 11kJ{mol}^{- 1}$