single+replacement+reactions

A single replacement reaction will involve an element in its natural state reacting with a compound. If the element is a metal, it will replace the metal in a compound; nonmetallic elements will replace nonmetals in compounds.

In order to predict the products of a single-replacement chemical reaction, use the following pattern:
 * A + BC --> AC + B

The letter pattern shown above should be used in predicting the arrangement of atoms in the products of a reaction.


 * Predicting products of a single replacement reaction using A + BC --> AC + B**

__Example:__ Predict the products of the reaction when copper metal is immersed in a solution of zinc chloride.

__Solution__:

Single replacement reactions always involve a lone element - in this case, copper. This is "A" in the reaction A + BC.

The "BC" is a compound, zinc chloride. Zinc is "B" and chloride is "C".

The reactant side of the equation is therefore:


 * Cu (s) + || Zn || Cl 2 (aq) || --> ||
 * A || B || C ||  ||

To predict the products, use the letter pattern AC + B. This would be copper chloride (AC) and zinc (B). Now complete the equation:


 * Cu (s) + || Zn || Cl 2 (aq) || --> || Cu || Cl 2 + || Zn ||
 * A || B || C ||  || A || C || B ||

The phases of the products can be predicted using the periodic table and the solubility rules. Zinc is a metal, and copper chloride is aqueous due to the chloride ion.

Final answer:


 * Cu (s) + || Zn || Cl 2 (aq) || --> || Cu || Cl 2 (aq) + || Zn (s) ||

__Predicting phases and molecular elements__

When an element is predicted as a product, its phase depends on the type of element it is; for example, metals will be solids (unless it is mercury).

Some nonmetallic elements are diatomic, meaning they have two atoms in their elemental state.

Here are the seven diatomic elements and their phases: hydrogen, H 2 (g) nitrogen, N 2 (g) oxygen, O 2 (g) fluorine, F 2 (g) chlorine, Cl 2 (g) bromine, Br 2 (l) iodine, I 2 (s)

Another common reaction is one that occurs between a chemically active metal and water:

metal + water --> hydrogen gas + metal hydroxide

Here is an example:

2 Na (s) + 2 H 2 O (l) --> H 2 (g) + 2 NaOH (aq)

Finally, be aware that nonmetals replace nonmetals:

F 2 (g) + 2 KI (s) --> Cl 2 (g) + 2 KF (s)

Try some practice problems:

Next: why do single replacement reactions work?