# How does zinc become oxidized when it's not in direct contact with copper ions in a galvanic cell?

Whenever a galvanic cell is explained in textbooks/videos, it usually starts by showing that if you put a piece of $\ce{Zn}$ in a $\ce{Cu^{2+}}$ ion solution, the $\ce{Zn}$ will become oxidized and transfer $\ce{2e-}$ to the $\ce{Cu^{2+}}$ ion, so the $\ce{Cu^{2+}}$ becomes a neutral $\ce{Cu}$ metal.

I understand this, but in a galvanic cell, the $\ce{Zn}$ never actually touches the $\ce{Cu^{2+}}$ ions, the $\ce{Zn}$ and $\ce{Cu}$ are only connected with wires. I don't understand how the $\ce{Zn}$ can be oxidized and transfer ions through the current.

Zinc electrode is anode and copper electrode is cathode. The two electrodes are connected by a electrically conducting wire. At anode, $\ce{Zn}$ atoms are oxidised to $\ce{Zn^2+}$ which go into the solution, and the electrons are left on the metal strip.

The electrons produced in the oxidation half-reaction at anode are transferred through the wire to $\ce{Cu}$ electrode where they are consumed. The $\ce{Cu^2+}$ ions are reduced to metallic $\ce{Cu}$ which coats on the $\ce{Cu}$ strip.

Thus, oxidation and reduction half reactions occur at separate electrodes and the current flows through the wire. A salt bridge maintains neutrality in both the compartments by a flow of ions.

The overall cell reaction can be given as:

$$\ce{Zn (s) + Cu^2+ -> Zn^2+ + Cu (s)}$$

• How can the Zink atoms be oxidized in the first place? How can some Zink that is just minding its own business,placed in a solution of Zinksulfat(away from the Copper ion solution), suddenly lose electrons? – IdiotThatNeedsHelp Feb 10 '15 at 16:59
• Because the dissociation of zinc into ions leads to decrease of its overall energy. The free energy change for this reaction is around $-213 kJ$ and as the entropy change isn't significant, the overall reaction is spontaneous. Also, It works in that direction and not the reverse (at standard conditions) because copper atoms are more closely and strongly bonded in the solid metal than zinc atoms. – Gokul Feb 10 '15 at 17:12
• So the zinc reacts with the zink ions in the zinksulfat solution and thus releases electrons? I thought that in order for an element to send electrons to another, the first element has to be lower in the galvanic series. – IdiotThatNeedsHelp Feb 10 '15 at 17:28
• No, the zinc does not react with the zinc ions. It dissociates into electrons as it is energetically favourable for it to dissociate rather than staying as a metal. – Gokul Feb 10 '15 at 17:37
• This process is thermodynamically governed by the Gibbs free energy equation. The equation is $\Delta{G} = \Delta{H} - T\Delta{S}$. For dissociation of zinc, the free energy is about $-213kJ$, thereby making it spontaneous. Read more here – Gokul Feb 11 '15 at 1:53