Difference Between Thermal Decomposition and Thermal Dissociation

Key Difference – Thermal Decomposition vs Thermal Dissociation 

Heat is a form of energy that can be transferred between two substances. Heat can be used to ionize a substance or to decompose a substance. The terms thermal decomposition and thermal dissociation are often used interchangeably. Although these terms express the same idea of separation of substances into counterparts, they are different from each other. The key difference between thermal decomposition and thermal dissociation is that thermal decomposition is the breakdown of large substances into smaller substances using heat whereas thermal dissociation is the ionization of a substance using heat.

CONTENTS

1. Overview and Key Difference
2. What is Thermal Decomposition
3. What is Thermal Dissociation
4. Similarities Between Thermal Decomposition and Thermal Dissociation
5. Side by Side Comparison – Thermal Decomposition vs Thermal Dissociation in Tabular Form
6. Summary

What is Thermal Decomposition?

Thermal decomposition is a form of chemical decomposition caused by heat. It is also known as thermolysis. The temperature at which the decomposition initiates is known as decomposition temperature. It is a multi-step process.

Decomposition involves the breakdown of chemical bonds. In order to break a chemical bond, energy should be given from outside. Therefore, a thermal decomposition is usually an endothermic reaction. The most common example for substances that undergo thermal decomposition is transition metal carbonates.

Example of Thermal Decomposition

• Calcium carbonate (CaCO₃) decomposes into calcium oxide (CaO) and carbon dioxide (CO₂) when heat is provided.

CaCO_3(s)→CaO_(s)  +   CO_2(g)

Figure 01: Calcium Carbonate Rocks

• Thermal decomposition of mercuric oxide gives mercury metal and oxygen.

2HgO    → 2Hg  +  O₂

• Thermal decomposition of iron oxide forms iron oxide and carbon dioxide.

FeCO₃→FeO  +  CO₂

What is Thermal Dissociation?

Thermal dissociation is the ionization of a substance using heat. The substance is separated into cationic and anionic counterparts. It is a single step process that includes the split of a substance into two parts. This reaction is usually a reversible process and one chemical bond is broken.

Figure 02: Dissociation of Methyl Bromide

The original compound can be obtained by cooling the reaction mixture since the process is reversible.

Example

CH₃Br     →     CH₃⁺+  Br^–

CH₃-CH₃ →CH₃⁺ +  CH₃^–

What is the Similarity Between Thermal Decomposition and Thermal Dissociation?

• Both Thermal Decomposition and Thermal Dissociation are processes that include the separation of a substance into small substances using heat energy.

What is the Difference Between Thermal Decomposition and Thermal Dissociation?

Summary – Thermal Decomposition vs Thermal Dissociation

Thermal decomposition and dissociation are two related terms that are often used interchangeably. But there are differences between these terms. The difference between thermal decomposition and thermal dissociation is that thermal decomposition is the breakdown of large substances into smaller substances using heat whereas thermal dissociation is the ionization of a substance using heat.

Reference:

1.“Thermal decomposition.” Wikipedia, Wikimedia Foundation, 17 Feb. 2018. Available here 
2.“Thermal decomposition .”  Study.com. Available here

Image Courtesy:

1.’Calcium carbonate rocks’By Ferdous – Own work, (CC BY-SA 3.0) via Commons Wikimedia 
2.’Heterolysis tert-Butyl Bromide V’By Jü – Own work, (Public Domain) via Commons Wikimedia 

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