http://www.ck12.org Chapter 11. Chemical Reactions
An example of this would be the reaction between zinc and hydrochloric acid, which produces zinc chloride and
hydrogen gas. Here is an image of this reaction:
FIGURE 11.7
Zinc metal reacting with a solution of hy-
drochloric acidThe balanced chemical equation for this single replacement reaction is shown below:
Zn(s)+2HCl(aq)→ZnCl 2 (aq)+H 2 (g)
Another type of single replacement reaction involves a solid metal replacing the metal cation in an ionic compound
that has been dissolved in water. If the solid metal is more reactive than the dissolved metal cations, the following
type of reaction can occur:
Metal + ionic solution→different metal + different ionic solution
A common example of this reaction is when iron is replaced by the more reactive zinc metal. The balanced chemical
equation for this process is shown below.
Zn(s)+FeSO 4 (aq)→Fe(s)+ZnSO 4 (aq)
Double Replacement Reactions
Double replacement reactions typically include two water-soluble salts that react with one another in solution. The
general form of a double replacement reaction would look something like the following:
AB+CD→AD+CB
Indouble replacement reactions, the cations from the original two ionic compounds trade anions to make two new
ionic compounds. In general, at least one of the new compounds must precipitate (form an insoluble solid) for us to
conclude that a reaction has occurred. An example of such a process is shown below with the double replacement
reaction between solutions of potassium iodide and lead(II) nitrate.
At the molecular level, our model for the way in which a precipitate forms can be described in an animation: