8.7 – NOTES Decomposition

C. Decomposition reactions a single compound breaks down to produce two or more products usually requires heat, light, or electricity; air bags inflating is a result of a decomposition reaction (sodium azide) difference b/t heating and burning – heating does not require oxygen, but burning does

1. Metallic chlorates will produce metal chlorides and oxygen gas; 2 NaClO3 (s) 2 NaCl (s) + 3 O2 (g) Ga(ClO3)3 (s) GaCl3 (s)+ 4.5 O2 (g)

2. Carbonates will produce a metal oxide and carbon dioxide; PbCO3 (s)  PbO (s) + CO2 (g) Al2(CO3)3 (s)  Al2O3 (s) + 3 CO2 (g)

REMEMBER FROM DOUBLE REPLACEMENTS iv. Reactions that form gases CO2, HCN, and H2S are the most common gases formed. Examples: 2HI(aq) + Li2S(aq)  H2S(g) + 2LiI(aq)   2HCl(aq) + Na2CO3(aq)  H2CO3(aq) + 2NaCl(aq) H2CO3(aq)  H2O(l) + CO2(g)

3. Metallic hydroxides will produce a metal oxide and water vapor 2 LiOH (s)  Li2O (s) + H2O (g) Ti(OH)4 (s)  TiO2 (s) + 2 H2O (g)

4. Certain acids will produce a nonmetallic oxide and water; these are the only two Chem I is responsible for knowing; acids are aqueous Carbonic acid H2CO3 (aq)  H2O (l)+ CO2 (g) Sulfurous acid H2SO3 (aq)  H2O (l)+ SO2 (g)

5. Certain metal oxides will produce the elements; metal must be an inactive metal or one with a low reactivity; Au, Ag, Pt, etc.; metal oxides are usually solid 2HgO (s)  2Hg (l) + O2 (g) 2Au2O3 (s)  4Au (s) + 3O2 (g)

6. Electrolysis of molten salts will produce the elements; molten means liquid Molten LiBr: 2LiBr (l)  2Li (l) + Br2 (l) CaCl2 (l) Ca (l) + Cl2 (g)