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Thermal Decomposition Reactions

Thermal Decomposition Reactions. Stable and Unstable Substances. Stable in Chemistry means unreactive in the conditions stated. Unstable means reactive in the conditions stated. Thermal Decomposition.

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Thermal Decomposition Reactions

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  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: CO2(g) CuCO3(s) CuO(s)

  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 H2O(g) Fe(OH)2(s) FeO(s) Green solid Black solid – changes to rust red on contact with air.

  11. Thermal Decomposition of Copper Hydroxide H2O(g) Cu(OH)2(s) CuO(s) Blue-Green solid Black solid

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