1. Objective

2. Heat is a very powerful form of energy. Although there are other forms of energy like light and electricity, heat is the most commonly used agent for initiating all chemical changes. Various classes of substances undergo decomposition to various extents when heated. This process is known as Thermal Decomposition. It gives rise to a number of newer products based on the conditions of temperature, pressure, operations etc. It is therefore important to understand the thermal behaviour pattern of most of the common class of compounds. Action of Heat on Substances

3. Oxides of Metals There are certain exceptional oxides that do decompose or change their colour on heating. The oxides of mercury and silver, when heated, decompose into their respective metals and oxygen.

4. Higher Oxides of Metals "Higher oxides are those oxides, which have more oxygen than the normal oxides."

5. Metals Carbonates Carbonates are compounds of various metals containing the carbonate radical CO 3 2-.

6. More Examples

7. Metals Bicarbonates Bicarbonates are compounds of various metals containing the bicarbonate radical. Bicarbonates when heated get decomposed to form their respective carbonates, water and carbon dioxide.

9. Metals Nitrates

12. Metals Sulphite Sulphite → Oxide + Sulphur dioxide

13. Metals Sulphate Sulphates are compounds of various metals containing the sulphate radical. Sulphates when heated very strongly decompose to give their respective oxides, sulphur dioxide and oxygen. Sulphate → Oxide + Sulphur dioxide + Oxygen

14. Metals Hydrous Salts The salts, which contain water of crystallisation are known as hydrous salts. When heated, they lose their water of crystallisation, and become anhydrous powders. They also lose their crystalline shape and sometimes their colour too.