$2{\mathrm{O}}_3\left(\mathrm{g}\right)\rightleftharpoons 3{\mathrm{O}}_2\left(\mathrm{g}\right)$

At $300 \mathrm{K}$, ozone is fifty percent dissociated. The standard free energy change at this temperature and $1 \mathrm{atm}$ pressure is $\left(-\right)......\mathrm{J} {\mathrm{mol}}^{-1}$. (Nearest integer)

[Given: $\ln 1.35=0.3$ and $\mathrm{R}=8.3 \mathrm{J}{ \mathrm{K}}^{-1}{ \mathrm{mol}}^{-1}$]