Is precipitation always involved in a double displacement reaction?

1 Answer
Jacob T.
Jun 9, 2018

Not necessarily.

Explanation:

There are a variety of spontaneous double displacement reactions. Some but not all of them involve the production of a precipitate.

For example, the neutralization reaction between hydrochloric acid #"HCl"# and sodium hydroxide #"NaOH"# counts as a double displacement reaction. However, this reaction produces no precipitate.

#"NaOH" (aq) + "HCl" (aq) color(navy)(to) "NaCl" (aq) + "H"_2"O"color(purple)((l))#

Neutralization reactions are feasible as double displacement reaction thanks to the production of water #"H"_2"O"#, a weak electrolyte that barely disassociate on its own. Meaning that as the reaction proceeds, the formation of water would act like a #"H"^(+)# / #"OH"^(-)# sink that continuously removes the two ions from the system.

Other types of reactions, such as those involving the evolution of a gas e.g., #"CO"_2# or #"NH"_3# can also be spontaneous. Here's a list of them on the English Wikipedia.

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