Single-Displacement Reaction

What Is a Single-Displacement Reaction?

Imagine replacing something that you own – a car, a battery or a cell phone. We typically replace these objects with something similar, but better, like the latest model of your phone. We replace our possessions because the replacements will better suit our purposes, or because they will serve us better in the future. This is comparable to single-displacement reactions in chemistry.

A single-displacement reaction, also known as a single-replacement reaction, is a type of chemical reaction where an element reacts with a compound and takes the place of another element in that compound. This type of reaction is typically pictured like this:

Activity Series of Metal and Nonmetals

Just like we said earlier, we usually replace something if the replacement is better or will suit our purposes better. The replacement is usually similar to the original object. In the same way, for a single-displacement reaction, an element can only be replaced if the element taking its place is more reactive. For single-displacement reactions, a metal replaces a metal, and a nonmetal replaces a nonmetal. In the periodic table, we can see where the metals and the nonmetals are located. The metals are located on the left side of the stairs and the nonmetals are located on the right side of the stairs.

How do we know which element can replace another? We refer to the activity series. This tells us the reactivity of metals and nonmetals. A more reactive metal replaces a less reactive metal. A more reactive nonmetal replaces a less reactive nonmetal.

If we look at the activity series of metals, we see that H is included, even though H is not a metal. This is because, for single-displacement reactions, H usually behaves like a metal in chemical reactions. In the activity series of metals, we can say that Li can replace K in a single-displacement reaction because Li is more reactive than K. The same can be said for nonmetals: F can replace Br in a single-displacement reaction because F is more reactive than Br. Br has relatively the same reactivity as O.

For example, in this reaction, Cu replaces Ag because Cu is more reactive than Ag. We can confirm that by looking at the activity series of metals.

It is always important to predict the products of the chemical reaction correctly and make sure that the final chemical equation is balanced. In this reaction, it shows how we balanced the chemical equation. We put a coefficient 2 in front of AgNO3 and Ag to balance the number of Ag atoms and NO3 atoms on both sides.

Now, in this chemical reaction, a more reactive nonmetal replaces a less reactive nonmetal. In this case, Cl replaces Br because Cl is a more reactive nonmetal.

We need to take note that when Cl replaced Br, Br has a subscript of 2 in the products side. This is because Cl and Br are both in the same group in the periodic table, so we know they behave similarly.

How to Complete a Single-Displacement Reaction

To complete a single-displacement reaction, we have to go through a few steps to make sure that our products and our final reaction are correct.

Step one: Determine if the reaction will occur.

The reaction will only proceed if the element that replaces the original element is more reactive. For this reaction, the question is, can Zn replace H? We need to refer to the activity series. This tells us that Zn can replace H, so this reaction will occur.

Step two: Determine the products.

When H is replaced by Zn, H will naturally occur as H2, so on the products side, one of the products is H2. Zinc, a metal, will combine with Cl, a nonmetal. Since Zn is in the second group on the periodic table, it will have a charge of +2. Since Cl is in the halogen group on the periodic table, we know it has a charge of -1.

We need to combine Zn and Cl atoms such that the sum of their charges is equal to zero. In this case, there will be 1 zinc atom and 2 chlorine atoms. Our products will then be ZnCl2 and H2.

Step three: Balance the chemical reaction.

In this reaction, the number of H atoms and Cl atoms are not balanced, so we need to balance them by putting coefficients in front of the reactants and products, as needed.