Consider an electrochemical cell: $A(s)∣∣∣ A_{n+}(aq,2M)∣∣∣ ∣∣∣ B2_{n+}(aq,1M)∣∣∣ B(s)$. The value of $△G_{θ}$ for the cell reaction is twice that of $△G_{θ}$ at 300 K. If the emf of the cell is zero, the $△G_{θ}∈JK?1mol_{?1}$ of the cell reaction per mole of B formed at 300 K is ____. (Given: ln(2) = 0.7, (universal gas constant) $=8.3JK?1mol_{?1}$. H, S and G are enthalpy, entropy and Gibbs energy, respectively.)