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Single-Displacement Reaction: Definition & Examples

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Lesson Transcript
Instructor: Nissa Garcia

Nissa has a masters degree in chemistry and has taught high school science and college level chemistry.

There are so many chemical reactions that occur around us that we classify them into different types. In this lesson, we will discuss single-displacement reactions, one of the main types of chemical reactions.

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:

Single-Displacement Reaction

Here, A replaces B in the compound BC. But how do we know which atoms or ions can replace each other? Let's discuss this in the following section.

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 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.

Metals and Nonmetals

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.

Activity Series

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.

Single Displacement: Metal

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.

Single Displacement: Nonmetal

We need to take note that when Cl replaces 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.

Zn and HCl Reaction

Step two: Determine the products.

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