Calculate standard internal energy change for $\mathrm{OF}_{2(\mathrm{~g})}+\mathrm{H}_2 \mathrm{O}_{(\mathrm{g})} \longrightarrow 2 \mathrm{HF}_{(\mathrm{g})}+\mathrm{O}_{2(\mathrm{~g})}$ at 300 K , if $\Delta_{\mathrm{f}} \mathrm{H}^{\circ}$ of $\mathrm{OF}_{2(\mathrm{~g})}, \mathrm{H}_2 \mathrm{O}_{(\mathrm{g})}$ and $\mathrm{HF}_{(\mathrm{g})}$ are 20, -250 and $-270 \quad \mathrm{~kJ} \mathrm{~mol}^{-1}$ respectively. $\left[\mathrm{R}=8.314 \mathrm{~J} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}\right]$

Calculate internal energy change of a system if work done by the system is 8 J and heat supplied to it is 40 J .