To determine if the reaction takes place spontaneously, we can use the standard cell potential formula:
E_{cell} = E_{cathode} - E_{anode}
Given the standard reduction potentials:
E^\circ_{\text{Ag}^+/\text{Ag}} = 0.80 \text{ V}
E^\circ_{\text{Cu}^{2+}/\text{Cu}} = 0.34 \text{ V}
The standard cell potential for the given reaction can be calculated as follows:
E_{cell} = E_{\text{cathode}} - E_{\text{anode}}
E_{cell} = E^\circ_{\text{Cu}^{2+}/\text{Cu}} - E^\circ_{\text{Ag}^+/\text{Ag}}
E_{cell} = 0.34 \text{ V} - 0.80 \text{ V}
E_{cell} = -0.46 \text{ V}
Since the calculated cell potential is negative (-0.46 V), the reaction does not occur spontaneously in the given direction.
To find the half-reactions for the new spontaneous reaction, we need to reverse the original half-reactions and the sign of their standard reduction potentials:
The half-oxidation reaction would be:
{\text{Ag} (s) \rightarrow Ag^+ (ac) + e^-}
E^\circ_{\text{new, Ag}^+/\text{Ag}} = -0.80 \text{ V}
The half-reduction reaction would be:
{\text{Cu}^{2+} (ac) + 2e^- \rightarrow Cu (s)}
E^\circ_{\text{new, Cu}^{2+}/\text{Cu}} = -0.34 \text{ V}
The new voltage of the cell for the spontaneous reaction can be calculated by subtracting the new anode half-reaction from the new cathode half-reaction:
E_{\text{cell, new}} = E_{\text{cathode}} - E_{\text{anode}}
E_{\text{cell, new}} = E^\circ_{\text{new, Cu}^{2+}/\text{Cu}} - E^\circ_{\text{new, Ag}^+/\text{Ag}}
E_{\text{cell, new}} = -0.34 \text{ V} - (-0.80 \text{ V})
E_{\text{cell, new}} = 0.46 \text{ V}
\boxed{E_{\text{cell, new}} = 0.46 \text{ V}}