I have received conflicting explanations for why the redox reaction in a galvanic cell occurs.
Some say that it occurs because the anodic metal dissolves more easily than the cathodic metal, and as such, the anodic metal will dissolve more quickly, becoming a positive cation that releases electrons (oxidizes). At the same time, in the cathodic half-cell, the positive cations in the solution will solidify on the surface of the cathode, due to rather wanting to be solid than an aqueous cation. However, these cations joining the cathode will add more positive charge than negative charge, and as such, the cathode will be positively charged. This will create a voltage between the electrons, and attract the electrons from the negatively charged anode, producing a current.
This means that the energy produced by a galvanic cell happens the system has less enthalpy when the anodic metal finds itself in a solution complex rather than a crystalline complex AND the cathodic metal finds itself in a crystalline complex rather than a solution complex.
Some say it occurs because of the reduction potential difference. The enthalpy change of an oxidation is always positive, and the enthalpy change of a reduction is always negative. If the cathodic ion's reduction has negative enough enthalpy change to make up for the positive enthalpy change of the anode's oxidation, then the reaction will happen. If the anode oxidized and the cathodic ion reduces, the resulting system will in total be of less enthalpy. Therefore, the redox reaction happens.
So, both explanations involve the fact that the energy of the system is lower if they react in the respective ways, but it has different explanations for exactly which process it is that involves the ultimately negative enthalpy change. Is it the solvation of the anode + the solidification of the cathode ion that produces the negative enthalpy change (and therefore the energy to be used), or is it the oxidation of the anode + the reduction of the cathode ion that produces the negative enthalpy change? Or is it a combination of both?
Looking at types of corrosion, there can happen a redox-reaction without an electrolyte (dry corrosion), which means solvation isn't necessary for redox in general, but perhaps is needed for a redox reaction to happen when the reactants aren't in physical contact.