\[
2 O _{3}( g ) \rightleftharpoons 3 O _{2}( g )
\]
At \( 300 K \), ozone is fifty percent dissociated. The standard free energy change at this temperature and \( 1 atm \) pressure is \( (-) \_ J mol ^{-1} \) (Nearest integer)
[Given: \( \ln 1.35=0.3 \) and \( R =8.3 J K ^{-1} mol ^{-1} \) ]
