Calculate the standard free energy change for the following reaction \[\] $Zn(s) + Cu^{2+} (aq) \rightarrow Cu(s) + Zn^{2+} (aq)$ \[\] Given that $ \Delta G_f^{\circ}\: for \: Cu^{2+} (aq)\: and \: Zn^{2+} (aq)$ as 65 kJ/mol and -147.2 kJ/mol respectively.