How do I predict the spontaneity of an ionic metathesis reaction? [closed]








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How do I predict the spontaneity of a [metathesis reaction](http://en.wikipedia.org/wiki/Metathesis_reaction)?


Is it a matter of summing up the differences between their ions' standard reduction potentials? 


Take the [salt metathesis reaction](http://en.wikipedia.org/wiki/Salt_metathesis_reaction) between two dissolved electrolytes; sodium chloride and silver nitrate (highlighted [here](http://en.wikipedia.org/wiki/Salt_metathesis_reaction#Aqueous_metathesis_.28precipitation.29)). While the [HSAB theory](http://en.wikipedia.org/wiki/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.




No, the spontaneity of the reaction does not have to do with the reaction potentials. All of the constituent parts of the salts exist as ions even in solid form, so there is no exchange of electrons occurring.


Rather, the insolubility of a salt is determined by the strength of the electrostatic forces between the ions. In some salts, the strength of the attractive forces that water applies is enough to break these ions apart, dissolving the salt. In other salts, the forces applied by the water might not be enough. These kinds of salts are those that are considered to be insoluble.


If you wish to predict whether or not a reaction between salts occurs (i.e. something precipitates out of solution), you should memorize the [solubility rules](http://www.chem.sc.edu/faculty/morgan/resources/solubility/).


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