Can metal displacement reactions happen with insoluable salts?

I know how normal metal displacement reactions work. If one metal is more reactive than the other, they will displace.


For example, normally for this reaction:
$$\ce{Fe\_{(s)} + 2AgCl\_{(aq)} -> Fe^{+2}\_{(aq)} + 2Ag\_{(s)} + 2Cl^{-}\_{(aq)}}$$


I would say that because the iron is more reactive than silver, the iron pushes it's electrons onto the silver.


But in this case, can this reaction depicted actually occur? Because $\ce{AgCl}$ is an insoluble salt. This means that the $\ce{Ag+}$ ions are not floating around to touch the iron metal. This means the reaction cannot occur.


I think in reality since $\ce{AgCl}$ can dissolve a little bit due to equilibrium, the reaction would go ahead, but if we pretend equilibrium dissolution doesn't occur, can this reaction proceed?


I think it can occur if the iron is touching the AgCl directly (allowing for conduction). I also think it cannot proceed if the iron was not touching the AgCl. Is this correct? For the purposes of answering my question, please ignore the solubility of AgCl.




In fact, at least on the basis of thermodynamics, a small amount of reaction between iron metal and "solid" silver chloride can be expected in water solvent.


This is because silver chloride is not completely insoluble in water. So if the thermodynamics is favorable, at least a small amount of reaction can occur.


First off, Ref. [1] quotes a standard reduction potential of -0.44 V for iron(II)/iron metal, versus +0.80 V for silver(I)/silver metal (all data and calculations are for 25°C and one atmosphere). Applying the Nernst Equation then gives the following equilibrium constant:


$\ce{2 Ag^+ + Fe <=> 2Ag + Fe^{2+}}, K = [\ce{Fe^{2+}}]/[\ce{Ag^+}]^2=8.5×10^{41}$


Taking silver chloride as having a solubility product of [$1.77×10^{-10}$](https://www.periodni.com/solubility_product_constants.html), we add in the dissolution reaction and render


$\ce{2 AgCl + Fe <=> 2Ag + Fe^{2+} + 2Cl^-}, K = [\ce{Fe^{2+}}][\ce{Cl^-}]^2=2.6×10^{22}$


This equilibrium condition is far beyond the range of concentrations/activities in a real aqueous ferrous chloride solution. So, what small amount of silver chloride dissolves into the water can undergo displacement favored by the large equilibrium constants above, producing ferrous chloride and silver metal, whereupon the removal of silver ion enables more silver chloride to dissolve. The reaction will eventually slow down due to accumulating chloride ions decreasing the solubility of the silver chloride, but the thermodynamics and mechanism are there for at least a little reaction to occur.


**References**


1.
Veleva L., “Soils and Corrosion” (Chapter 32), in *Corrosion Tests and Standards: Application and Interpretation*, 2nd Edition, R. Baboian Ed., ISBN: 0-8031-2058-3, ASTM International, OH, pp.387-404, 2005.


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