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.

  • 2
    $\begingroup$ Your question is confusing - I have no idea why you're mixing simple precipitation with redox - there's no redox in there! $\endgroup$
    – Mithoron
    May 9, 2015 at 15:01
  • $\begingroup$ @Mithoron: Read about salt metathesis reactions here. $\endgroup$ May 9, 2015 at 15:18
  • 1
    $\begingroup$ I'm well aware how metathesis works and it's driven by precipitation or vaporisation or complexation $\endgroup$
    – Mithoron
    May 9, 2015 at 17:53

1 Answer 1


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.

  • $\begingroup$ This does not answer my question. I am specifically asking about metathesis reactions. $\endgroup$ May 9, 2015 at 15:26
  • 1
    $\begingroup$ @VatsalManot Which part? I responded to the fact this is not a redox reaction, so the use of reduction potentials is meaningless. $\endgroup$
    – ringo
    May 9, 2015 at 15:30
  • $\begingroup$ The main question: How do I predict the spontaneity of a metathesis reaction? All you have done is nullify my proposed method. $\endgroup$ May 9, 2015 at 15:36
  • 1
    $\begingroup$ @VatsalManot Does the list of solubility rules not answer that question? If one of the product salts is insoluble, the reaction occurs. If both of the product salts are soluble, there is no reaction. $\endgroup$
    – ringo
    May 9, 2015 at 16:00

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