Page 130 - ICSE Chemistry 8

Some more examples of thermal decomposi on are listed here.
Heat
• 2FeSO (s) Fe O (s) + SO (g)  + SO (g) 
2
4
3
2
3
Ferrous sulphate Ferric oxide Slphur dioxide Sulphur trioxide
(reddish-brown residue)
Heat
• 2HgO(s) 2Hg(s) + O (g) 
2
Mercury(II) oxide Mercury Oxygen
Heat
• 2Pb(NO ) (s) 2PbO(s) + 4NO (g) + O (g) 
2
2
3 2
Lead nitrate Lead monoxide Nitrogen dioxide Oxygen
(white) (yellow) (reddish-brown fumes)
The decomposi on brought about by electricity is called electroly c decomposi on.
Examples:
• Decomposi on of water: When an electric current is passed through water, it decomposes to give
hydrogen and oxygen.
Electricity
2H O(l) 2H (g)  + O (g) 
2
2
2
Water Hydrogen Oxygen
• Decomposi on of sodium chloride: When an electric current is passed through a solu on of
sodium chloride, it dissociates to sodium and chlorine.
Electricity
2NaCl(molten) 2Na(s) + Cl (g) 
2
Sodium chloride Sodium Chlorine
• Decomposi on of aluminium oxide: When an electric current is passed through molten aluminium
oxide, it decomposes to form aluminium and oxygen.
Electricity
2Al O 4Al(s) + 3O (g) 
2
3
2
Aluminium oxide Aluminium Oxygen
(molten)
The decomposi on brought about by light is called photoly c decomposi on.
Examples:

• Decomposi on of silver chloride: When silver chloride is exposed to light, it decomposes to form
silver metal and chlorine gas.
light
2AgCl(s) 2Ag(s) + Cl (g) 
2
Silver chloride Silver Chlorine
(white) (greyish-white) (greenish-yellow)

• Decomposi on of silver bromide: Silver bromide on exposure to light decomposes to form silver
and bromine gas.
light
2AgBr(s) 2Ag(s) + Br (g) 
2
Silver bromide Silver Bromine
Activity 6.5

Aim: To show thermal decomposi on of ammonium chloride
Materials required: Some ammonium chloride, a test tube, a burner

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