Chemical decomposition is defined as the breakdown of a compound into simpler compounds or its basic elements. This type of chemical reaction occurs when a chemical is exposed to extreme environmental conditions like heat, radiation, humidity or acidity in a particular solvent. A chemical decomposition is much more than just a change in the physical state of a material. When a physical state of a material changes, for example an ice cube melts in to liquid water, or liquid water boils into steam, the basic chemical formula remains the same. However, when a chemical decomposition takes place, for example the electrolysis of water, not only does its physical state change, its chemical formula breaks down into its individual elements as well. The chemical decomposition that takes place during the electrolysis of water is defined in the following equation:
2 H2O(I) → 2 H2 + O2
In this example, a molecule of water breaks down into its individual elements i.e. hydrogen and oxygen. The physical state of water also changes, from liquid into gases. Chemical decomposition can be both, either endothermic or exothermic. The exothermic chemical decomposition is generally terms as a thermal decomposition which is caused by applying heat to a particular chemical. The decomposition temperature of a substance is the temperature at which a chemical breaks down or decomposes. Thermal decomposition is the most general form of chemical decomposition that occurs practically everywhere in the environment. Burning of fossil fuels, condensation of rain from water vapor, the setting of cement and concrete, mixing of water and strong acids, reactions between acids and alkalis are all categorized as exothermic decomposition reactions.
On the other hand, an endothermic decomposition reaction is where heat is applied to a particular compound in order to break the covalent bonds between its molecules. An example that explains an endothermic process is once again water. As described earlier, water can be reduced or decomposed to its basic elements through electrolysis. However, the same result can also be achieved through endothermic decomposition. Water, when heated to 2000C decomposes into its constituent elements. Apart from this, various other examples like melting solid salts, making a anhydrous salt from a hydrate are also very prominent examples of endothermic chemical decomposition.