Types of Chemical Reactions: Single Replacement

Lesson Plan - Get It!

Audio:

A coach may substitute players in and out during a game, based on the skill set of each member.

Changing the composition of the team can lead to a change in the score! There is a chemical reaction where elements replace one another in compounds, called a single-replacement reaction.

Single-replacement reactions follow the pattern: A + BC —> B + AC

A good example of a single-replacement reaction is the formation of sodium hydroxide: 2Na + 2HOH —> 2NaOH + H₂. Notice that the hydrogen is replaced with a sodium atom.

In a single-replacement reaction, the element that replaces another must be more reactive. That means it is more likely to bond with other elements.

• So, how do you know if an element is more reactive than another?

Well, you can use a tool called the reactivity series to determine the reactivity of different elements.

Check out the Reactivity series page, from the British Broadcasting Corporation, to see an image of the reactivity series of metals.

• What do you notice about the way the metals are organized?

You shouldn't need to click through multiple pages, but you can read the material for more information.

In an single-replacement reaction, the replacement element must be more reactive than the element it is replacing. For example, potassium can replace almost any other metal, while gold doesn't replace many metals. Remember that metals are cations, or positively-charged particles. Cations can only replace cations, and anions can only replace anions.

If the replacement element is less reactive, the reaction will not run. The reaction equation would be A + BC —> no reaction.

Single-replacement reactions run when one element works to replace another element held in a chemical bond. In order to break the existing bond, the replacement element must be more reactive.

• What tool do you use to check the reactivity of the element?

The reactivity series helps you know if the reaction will run.

• What do you write if the reaction does not run?

You write the equation yielding no reaction. Write a one-sentence summary of how the reactivity series is used in chemistry.

In the Got It? section, practice using the reactivity series to determine if the reaction runs.