Replacement Reactions
Jean Brainard, Ph.D.
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Printed: August 25, 2016
AUTHOR
Jean Brainard, Ph.D.
www.ck12.org
C HAPTER
Chapter 1. Replacement Reactions
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Replacement Reactions
• Define replacement reaction.
• Contrast single and double replacement reactions.
• Give examples of single and double replacement reactions.
What a job! The man hanging from the burning helicopter in the photo above is a stunt man. He fills in for the
lead actor in the movie in dangerous scenes like this one. Like other stunt workers, he has special training to do
such dangerous work as safely as possible. Replacing actors with stunt workers is common in action movies. Some
chemical reactions also involve replacements. More reactive elements replace less reactive elements in compounds.
These reactions are called replacement reactions.
What Is A Replacement Reaction?
A replacement reaction occurs when elements switch places in compounds. This type of reaction involves ions
(electrically charged versions of atoms) and ionic compounds. These are compounds in which positive ions of a
metal and negative ions of a nonmetal are held together by ionic bonds. Generally, a more reactive element replaces
an element that is less reactive, and the less reactive element is set free from the compound. There are two types of
replacement reactions: single and double. Both types are described below.
Q: Can you predict how single and double replacement reactions differ?
A: One way they differ is that a single replacement reaction involves one reactant compound, whereas a double
replacement reaction involves two reactant compounds. Keep reading to learn more about these two types of
reactions.
Single Replacement Reactions
A single replacement reaction occurs when one element replaces another in a single compound. This type of reaction
has the general equation:
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A + BC → B + AC
In this equation, A represents a more reactive element and BC represents the original compound. During the reaction,
A replaces B, forming the product compound AC and releasing the less reactive element B.
An example of a single replacement reaction occurs when potassium (K) reacts with water (H2 O). A colorless solid
compound named potassium hydroxide (KOH) forms, and hydrogen gas (H2 ) is set free. The equation for the
reaction is:
2K + 2H2 O → 2KOH + H2
In this reaction, a potassium ion replaces one of the hydrogen atoms in each molecule of water. Potassium is a highly
reactive group 1 alkali metal, so its reaction with water is explosive.
Q: Find potassium in the periodic table of the elements. What other element might replace hydrogen in water in a
similar replacement reaction?
A: Another group 1 element, such as lithium or sodium, might be involved in a similar replacement reaction with
water.
Double Replacement Reactions
A double replacement reaction occurs when two ionic compounds exchange ions. This produces two new ionic
compounds. A double replacement reaction can be represented by the general equation:
AB + CD → AD + CB
AB and CD are the two reactant compounds, and AD and CB are the two product compounds that result from the
reaction. During the reaction, the ions B and D change places.
Q: Could the product compounds be DA and BC?
A: No, they could not. In an ionic compound, the positive metal ion is always written first, followed by the negative
nonmetal ion. Therefore, A and C must always come first, followed by D or B.
An example of a double replacement reaction is sodium chloride (NaCl) reacting with silver fluoride (AgF). This
reaction is represented by the equation:
NaCl + AgF → NaF + AgCl
During the reaction, chloride and fluoride ions change places, so two new compounds are formed in the products:
sodium fluoride (NaF) and silver chloride (AgCl).
Q: When iron sulfide (FeS) and hydrogen chloride (HCl) react together, a double replacement reaction occurs. What
are the products of this reaction? What is the chemical equation for this reaction?
A: The products of the reaction are iron chloride (FeCl2 ) and hydrogen sulfide (H2 S). The chemical equation for this
reaction is:
FeS + 2HCl → H2 S + FeCl2
Summary
• A replacement reaction occurs when elements switch places in compounds. This type of reaction involves
ions. Generally, more reactive elements replace less reactive elements.
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Chapter 1. Replacement Reactions
• A single replacement reaction occurs when one element replaces another element in one compound. This type
of reaction is represented by: A + BC → B + AC.
• A double replacement reaction occurs when two ionic compounds exchange ions, producing two new ionic
compounds. This type of reaction is represented by: AB + CD → AD + CB.
Review
1. What is a replacement reaction?
2. Compare and contrast single and double replacement reactions, and give the general equation for each type of
reaction.
3. Which of the following reactions is not a replacement reaction?
a.
b.
c.
d.
Fe + CuSO4 → FeSO4 + Cu
2Na + 2H2 O → 2NaOH + H2
Zn + 2HCl → ZnCl2 + H2
2Na + Cl2 → 2NaCl
Resources
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URL: https://www.ck12.org/flx/render/embeddedobject/185352
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