Difference Between Double Displacement and Double Decomposition Reaction

The key difference between double displacement and double decomposition reaction is that the double displacement reactions are chemical reactions in which the components of two reactants replace each other whereas the double decomposition reactions is a form of double displacement reactions in which one or more reactants does not dissolve in the solvent.

Both terms “double displacement” and “double decomposition” reactions explain the same type of chemical reactions, except, the “double decomposition” is a much older term. Therefore, this older term has been largely replaced by the new term, “double displacement” because this term explains the actual idea of the reaction; a displacement. Moreover, we used the older term when one or more reactants does not dissolve in the solvent.

CONTENTS

1. Overview and Key Difference
2. What is Double Displacement Reaction
3. What is Double Decomposition Reaction
4. Side by Side Comparison – Double Displacement vs Double Decomposition Reaction in Tabular Form
5. Summary

What is Double Displacement Reaction?

Double displacement reactions are a type of chemical reactions in which the components of two reactants replace each other to form new products. In these reactions, the cation and anions tend to undergo this displacement. Typically, the end product of these reactions is a precipitate. Therefore, the end product is entirely different from the reactants.

We can write a general equation for a double displacement reaction as follows.

A-B     +      C-D          →        C-B      +      A-D

In the above equation, A and C components of each reactant have switched their places. Generally, these reactions occur in aqueous solutions. Furthermore, we can categorize these reactions as follows;

1. Precipitation reactions – A precipitate forms at the end of the reaction. For example, the reaction between silver nitrate and sodium chloride forms silver chloride precipitate and aqueous sodium nitrate.
2. Neutralization reactions – An acid neutralizes upon the reaction with a base. For examples, an HCl solution (acid) can be neutralized from a NaOH solution (base).

What is Double Decomposition Reaction?

Double decomposition reactions are a type of double displacement reactions in which one or more reactants are insoluble in the solvent. However, people often used this term as the older version of double displacement reactions. As an example, the reaction between zinc sulfide and hydrochloric acid forms zinc chloride and hydrogen sulfide gas. There, zinc sulfide is in the solid state, undissolved in the aqueous medium.

What is the Difference Between Double Displacement and Double Decomposition Reaction?

Double displacement reactions are a type of chemical reactions in which the components of two reactants replace each other to form new products. We use the term double decomposition reactions as the older name of double displacement reactions. However, we use this term to name displacement reactions that involve one or more reactants, which are insoluble in the solvent. The below infographic presents the difference between double displacement and double decomposition reaction in tabular form.

Summary – Double Displacement vs Double Decomposition Reaction

Both double displacement and double decomposition reactions describe the same mechanism of a particular type of chemical reactions. However, they differ from each other according to the nature of reactants as well as the use of the term. The difference between double displacement and double decomposition reaction is that the double displacement reactions are chemical reactions in which the components of two reactants exchange with each other whereas the double decomposition reactions is a form of double displacement reactions in which one or more reactants does not dissolve in the solvent.

Reference:

1. “Our Objective.” Decomposition Reaction (Resources) : Class 10 : Chemistry : Amrita Online Lab. Available here 
2. Helmenstine, Anne Marie. “What Is a Double Displacement Reaction?” ThoughtCo, ThoughtCo. Available here

Image Courtesy:

1.”Silver chloride by Danny S. – 001″By Danny S. – Own work, (CC BY-SA 3.0) via Commons Wikimedia