Prediction and significance of cell potentials

Given the values for two half reactions, you can easily predict the potential difference of the corresponding cell simply add the reduction potential of the reduction half-cell to the negative of the reduction potential (that is, to the oxidation potential) of the oxidation reaction. 

Solution. The net reaction corresponding to this cell will be 

Since this involves the reverse of the AgCl reduction, we must reverse the corresponding half-cell potential  

Since this potential is positive, tthe reaction will proceed to the right electrons will be withdrawn from the copper electrode and flow through the external circuit into the silver electrode. Note carefully that in combining these half-cell potentials, we did not multiply E° the for the Cu2+/Cu couple by two. The reason for this will be explained later. 

The activity series has long been used to predict the direction of oxidation-reduction reactions. Consider, for example, the oxidation of Cu by metallic zinc that we have mentioned previously. The fact that zinc is near the top of the activity series means that this metal has a strong tendency to lose electrons. By the same token, the tendency of Zn to accept electrons is relatively small. Copper, on the other hand, is a poorer electron donor, and thus its oxidized form, Cu, is a fairly good electron acceptor. We would therefore expect the reaction 

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