Recognize invernessgangshow.netical reactions as single-replacement reactions and double-replacement reactions. Use the periodic table, an activity series, or solubility rules to predict whether single-replacement reactions or double-replacement reactions will occur.

You are watching: In order to predict whether or not a single replacement reaction takes place

Up until now, we have presented invernessgangshow.netical reactions as a topic, but we have not discussed how the products of a invernessgangshow.netical reaction can be predicted. Here we will begin our study of certain types of invernessgangshow.netical reactions that allow us to predict what the products of the reaction will be.

A single-replacement reaction is a invernessgangshow.netical reaction in which one element is substituted for another element in a compound, generating a new element and a new compound as products. Presented below:

\<\ce{2HCl(aq) + Zn(s) → ZnCl2(aq) + H2(g)}\nonumber \>

is an example of a single-replacement reaction. The hydrogen atoms in \(\ce{HCl}\) are replaced by \(\ce{Zn}\) atoms, and in the process a new element—hydrogen—is formed. Another example of a single-replacement reaction is

\<\ce{2NaCl(aq) + F2(g) → 2NaF(s) + Cl2(g)}\nonumber \>

Here the negatively charged ion changes from chloride to fluoride. A typical characteristic of a single-replacement reaction is that there is one element as a reactant and another element as a product.

Not all proposed single-replacement reactions will occur between two given reactants. This is most easily demonstrated with fluorine, chlorine, bromine, and iodine. Collectively, these elements are called the halogens and are in the next-to-last column on the periodic table (Figure \(\PageIndex{1}\)). The elements on top of the column will replace the elements below them on the periodic table, but not the other way around. Thus, the reaction represented by

\<\ce{CaI2(s) + Cl2(g) → CaCl2(s) + I2(s)}\nonumber \>

will occur; but the reaction

\<\ce{CaF2(s) + Br2(ℓ) → CaBr2(s) + F2(g)}\nonumber \>

will not, because bromine is below fluorine on the periodic table. This is just one of many ways the periodic table helps us to understand invernessgangshow.netistry.

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api/deki/files/90661/4856feea642ad7543b114732b2b5fc1e.jpg?revision=1&size=bestfit&width=424&height=452" />Figure \(\PageIndex{2}\): Double-Replacement Reactions. Some double-replacement reactions are obvious because you can see a solid precipitate coming out of solution. Source: Photo courtesy of Choij,