Why are precipitation reactions irreversible?

[Entanglement]

Why are precipitation reactions are irreversible as NaCl + AgNO3 --------> AgCl + NaNO3

 

[Simon Bridge]

Because of the changes involved.

Why would you expect they might be?

 

[JeffEvarts]

OK, let's try that again with a bit more depth

As long as salts are in solution, they tend to separate as ions. Consider sodium chloride or potassium carbonate... they dissociate (wrong word?) like husbands and wives at a party, each wandering around within the group: Na+, K+, Cl- and CO3-. They meet one another, separate, and go on their merry ways.

But when something LEAVES solution (as a solid) it stops being separate ions... it's a compatible pair at a singles dance leaving for dinner together. Once they leave solution, they're not separate entities mingling, they're a pair on their own.

OK, analogies are bogus, but that's the basic idea: they're only intermixing ions while dissolved in solution.

 

[Entanglement]

Yeah I got it, so the reaction could occur the salt must exist as ions, but precipitates are insoluble solids do they won't react again

 

[Borek]

Yeah I got it, so the reaction could occur the salt must exist as ions, but precipitates are insoluble solids do they won't react again

Add enough water and they will be dissolved back.