1. Thermal Decomposition Reactions

2. Stable and Unstable Substances Stable in Chemistry means unreactive in the conditions stated. Unstable means reactive in the conditions stated.

3. Thermal Decomposition When 2 elements combine to form a compound, the product requires heat energy for the elements to be reformed. i.e. the compound is more stable than the elements at room temperature. Many compounds undergo thermal decomposition – the compound breaks up into compounds of lower mass, or into its elements.

4. Thermal Decomposition The thermal stability of a metal compound is directly related to the chemical activity of the metal. –Sodium compounds are the most thermally stable. –Gold compounds do not exist because they are thermally unstable.

5. Activity Series of Metals By observing the reaction of metals with oxygen, acid and water, it is possible to arrange the metals in an order of activity. This is the activity series. Potassium > Sodium > Lithium > Calcium > Magnesium > Aluminium > Zinc > Iron > Lead > (hydrogen) > Copper > Silver > Gold

6. Metal Carbonates and Metal Hydrogen Carbonates The conditions required for the decomposition of metal carbonates and metal hydrogen carbonates depend on the chemical activity of the metal –Sodium and potassium carbonate are thermally stable and can not be decomposed by heating.

7. Metal Carbonates and Metal Hydrogen Carbonates Highly reactive metals form stable compounds that require high energy to undergo thermal decomposition. –Calcium carbonate – the high reactivity of calcium metal results in a stable compound and thus high energy is needed to decompose calcium carbonate.

8. Thermal Decomposition of Copper Carbonate Copper is low in the activity series so, copper carbonate is thermally decomposed with low energy. The equation is: CuCO 3(s) CuO (s) CO 2(g)

9. Thermal Decomposition of Copper Carbonate Copper carbonate is a green powder, on gentle heating, it decomposes into copper oxide, a black powder and carbon dioxide gas.

10. Thermal Decomposition of Iron II Hydroxide Fe(OH) 2(s) FeO (s) H 2 O (g) Green solid Black solid – changes to rust red on contact with air.

11. Thermal Decomposition of Copper Hydroxide Cu(OH) 2(s) CuO (s) H 2 O (g) Blue-Green solid Black solid