For the following reaction at $50^{\circ} \mathrm{C}$ and at 2 atm pressure, $$ 2 \mathrm{~N}_2 \mathrm{O}_5(\mathrm{~g}) \mathrm{f} \quad 2 \mathrm{~N}_2 \mathrm{O}_4(\mathrm{~g})+\mathrm{O}_2(\mathrm{~g}) $$ $\mathrm{N}_2 \mathrm{O}_5$ is $50 \%$ dissociated. The magnitude of standard free energy change at this temperature is $x$. $x= \mathrm{Jmol}^{-1}$ [Nearest integer]. Given: $\mathrm{R}=8.314 \mathrm{~J} \mathrm{~mol}^{-1} \mathrm{~K}^{-1}, \log 2=0.30, \log 3=0.48, \ln 10=2.303,{ }^{\circ} \mathrm{C}+273=\mathrm{K}$