$40^{\circ}$ of HI undergoes decomposition to $\mathrm{H}_2$ and $\mathrm{I}_2$ at $300 \mathrm{~K} . \Delta \mathrm{G}^{\ominus}$ for this decompostion reaction at one atmosphere pressure is $\_\_\_\_$ $\mathrm{J} \mathrm{mol}^{-1}$. [nearest integer] (Use $\mathrm{R}=8.31 \mathrm{~J} \mathrm{~K}^{-1} \mathrm{~mol}^{-1} ; \log 2=0.3010 . \ln 10=2.3, \log 3=0.477$ )