How do I predict the spontaneity of a metathesis reaction?
Is it a matter of summing up the differences between their ions' standard reduction potentials?
Take the salt metathesis reaction between two dissolved electrolytes; sodium chloride and silver nitrate (highlighted here). While the HSAB theory exists, it has not been quantified yet (as far that I know of).
Based my current knowledge of Chemistry, I would expect something like this:
Let the symbol of each element represent its standard reduction potential. Then spontaneity would be given by the following:
$\ce{((-Na) - (-Ag)) + (Cl - NO3)}$
Where a positive value would imply that the reaction is spontaneous, and the magnitude the degree of spontaneity.