Stable and Unstable Substances Stable in Chemistry means unreactive in the conditions stated Unstable means reactive in the conditions stated Thermal Decomposition When 2 elements combine to form a compound the product requires heat energy for the elements to be reformed ID: 234201
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Slide1
Thermal Decomposition ReactionsSlide2
Stable and Unstable Substances
Stable in Chemistry means
unreactive
in the conditions stated.
Unstable means reactive in the conditions stated.
Slide3
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.Slide4
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.Slide5
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 > GoldSlide6
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 metalSodium and potassium carbonate are thermally stable and can not be decomposed by heating.Slide7
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. Slide8
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)Slide9
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.Slide10
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.Slide11
Thermal Decomposition of
Copper HydroxideCu(OH)
2(s)
CuO
(s)
H
2
O
(g)
Blue-Green solid
Black solid