Reaction Prediction?

1 Answer
May 25, 2017
  1. #"KOH (aq)" rarr "K"^+ "(aq)" + "OH"^(-) "(aq)"#

  2. #"AlCl"_3 "(aq)" + "3AgNO"_3 "(aq)" rarr "Al"("NO"_3)_3 "(aq)" + 3"AgCl (s)"#



The first reaction is the decomposition of potassium hydroxide. In aqueous solution, this compound (along with all strong electrolytes/ionic compounds) will dissociate into its component ions, #"K"^+# and #"OH"^-#:

#"KOH (aq)" rarr "K"^+ "(aq)" + "OH"^(-) "(aq)"#


In this reaction, aluminum chloride and silver nitrate are mixed in aqueous solution. Remember that for double replacement reactions, a reaction will not occur if all the ions in the complete ionic equation are the same on both sides of the reaction arrow.

Why? Because the only thing that happened was simply the solutes being dissolved; no products form, as there's no driving force (a precipitate) to cause these dissociated ions to form anything, so they just remain as ions in solution. (Dissolution is not a chemical change).

An easy way to determine if a reaction occurs or not is to look at the molecular equation: if all the components are well-soluble (they have an #"(aq)"# after it), there's no reaction occurring there, as the ions are just dissolved. There will be a reaction if a solid precipitate is formed (a product with an #"(s)"#). The equation for this reaction is

#"AlCl"_3 "(aq)" + "3AgNO"_3 "(aq)" rarr "Al"("NO"_3)_3 "(aq)" + 3"AgCl (s)"#

Since a solid precipitate formed, a chemical reaction indeed occurred. The net ionic equation for this reaction is

#"Ag"^+ "(aq)" + "Cl"^(-) "(aq)" rarr "AgCl (s)"#

The coefficients were reduced to lowest terms.