For a cell reaction, ${\mathrm{Cu}}^{2+}({\mathrm{C}}_1,\mathrm{aq})+{\mathrm{Zn}}_{\left(\mathrm{s}\right)}\to {\mathrm{Zn}}^{2+}({\mathrm{C}}_2,\mathrm{aq})+{\mathrm{Cu}}_{\left(\mathrm{s}\right)},$ of an electro chemical cell, the change in standard free energy, $\Delta G^0$ at a given temperature is

From given data 

Anodic reaction             $Zn\to Z{n}^{+2}+2e^{-}$

Cathodic reaction           $C{u}^{+2}+2e^{-}\to Cu$

                                   ----------------------------------

                                    $Zn+C{u}^{+2}\to Z{n}^{+2}+Cu$

According to Nernst euation

$E^{ }{ }_{Cell}=E^0{ }_{Cell}-\frac{0.059}{n}\frac{\left[Z{n}^{+2}\right]}{\left[C{u}^{+2}\right]}$

$E^{ }{ }_{Cell}-E^0{ }_{Cell}$  gives  change  in Gibbs free energy of reaction since

$\Delta G^0$  and $E^0$  related as  $\Delta G^0=nF{E}^0$

So change in Gibbs free energy   =$\frac{0.0591}{2}\log \frac{C_2}{C_1}$

                                                                           n= no of electrons involved

                                                                                    F=Faraday (36500 C) of charge

                                                                                 $\frac{2.303RT}{F}=0.059V$