Chemical Reactions and Equations - Class 10th Science
Thermal Decomposition
Reaction in which energy is absorbed either in the form of heat, light or electricity is called thermal decomposition reaction.
In decomposition reactions discussed above, decomposition took place after absorption of energy. Hence, all those reactions are known as thermal decomposition.
Thermal means "heat" and decomposition means to break down, because of this they are called thermal decomposition. This means decomposition because of getting heat.
Exothermic and Endothermic Reaction
Apart from the breaking and making of chemical bonds between atoms, in a chemical reaction either heat is evolved or is absorbed. On the basis of evolution and absorption of heat chemical reaction can be divided into the following two types:
- Exothermic Reaction
- Endothermic Reaction
Exothermic Reaction
Chemical reactions in which heat is evolved are called Exothermic Reactions.
Example:
When quick lime (Calcium oxide) reacts with water, calcium oxide is formed and heat evolved.
Since, heat evolved in this reaction, thus it is an exothermic reaction.
Example:
Burning of coal gives lot of heat. This is an example of exothermic reaction.
Example:
Burning of natural gas is an example of exothermic reaction. Similar to burning of coal, burning of natural gas also gives heat.
Example: Respiration
We respire to live. Respiration gives us energy. In respiration a reaction takes place in our body which release energy. When we respire glucose burns and gives energy. Since, respiration gives energy, thus it is an exothermic reaction.
Endothermic Reaction:
Reactions in which heat is absorbed are called Endothermic Reactions. All of the decomposition reactions require energy in any form, thus all of them are known as endothermic reactions. Thermal decompositions are also known as endothermic reactions.
Example: