1. TYPES OF
CHEMICAL
REACTIONS

2. 1. Combination Reactions
Also known as composition or synthesis reactions.
Two or more simple substances combine to form one substance

3. GENERAL EQUATION: A + B  AB
Examples:
2 Mg (s) + O2(g)  2 MgO(s)
Metal + oxygen  metallic oxide
MgO(s) + H2O (l)  Mg(OH)2(l)
Metallic oxide + water  base
C(s) + O2 (g)  CO2(g)
Non-metal + oxygen  non-metallic oxide
CO2(g) + H2O (l)  H2CO3(l)
Non-metal oxide + water  acid

4. 2. DECOMPOSITION REACTIONS
Opposite of combination reactions
Involves the breakdown of a substance into two or more simple substances
Requires energy to decompose the substance
GENERAL EQUATION: AB  A+B Δ Δ

5. 6 TYPES OF DECOMPOSITION REACTIONS
a. Metallic chlorates, when heated, decomposed into metallic chloride and oxygen gas
2 KClO3(s)  2 KCl(s) + 3 O2(g)
b. Metallic carbonates, when heated, are decomposed into metallic oxides and carbon dioxide
CaCO3(s)  CaO(s) + CO2(g) Δ Δ

6. Ca(OH)2 (aq)  CaO(s) + H2O(g)
c. Many metallic hydroxides, when heated, breakdown into metallic oxides and water.
Ca(OH)2 (aq)  CaO(s) + H2O(g)
Exception NaOH and KOH
d. Some acids, when heated, break down into nonmetallic oxides and water.
H2CO3(aq)  CO2(g) + H2O(l) Δ Δ

7. 2 HgO(s)  2 Hg (l) + O2(g) 2 PbO2 (s)  2 PbO (s) + O2(g)
e. Some oxides, when heated decomposed. There are only few exceptions since many oxides are very stable.
2 HgO(s)  2 Hg (l) + O2(g)
2 PbO2 (s)  2 PbO (s) + O2(g)
f. Some decomposition reactions are brought about by electricity in decomposition reactions called electrolysis .
2 H2O(l)  2 H2(g) + O2(g)
2 NaCl(s)  2 Na(s) + Cl2(g) Δ Δ Δ Δ

8. 3. SINGLE REPLACEMENT REACTIONS
Also known as substitution reactions;
An uncombined element replaces another element in a given compound.
The uncombined element must have a greater activity series value compared to the combined element (see table)

9. GENERAL EQUATION: A + XY  AY + X The free element (A) is a metal replacing another metal in a salt or hydrogen in an acid.
Examples:
Cu(s) + AgNO3(aq)  CuNO3(aq) + Ag(s)
Zn(s) + 2HCl (aq)  ZnCl2(aq) + H2(g)
GENERAL EQUATION: B + XY  XB + Y The free element (B) is a nonmetal replacing another nonmetal in a salt or in an acid.
Examples:
Cl2(g) + 2 NaBr(aq)  2 NaCl (aq) + Br2(g)
F2(g) + 2 HBr (aq)  2 HF(aq) + Br 2(g)

10. 4. Double Replacement Reactions
Involves an exchange of ions between reactants
A cation in one compound replaces the cation in a second compound resulting to the formation of two new compounds

11. 2 NaCl(aq) + K2SO4(aq)  Na2SO4(aq) + 2KCl(aq)
GENERAL EQUATION: AB + XY  AY + XB The cation A replaces another cation X in a salt or hydrogen in an acid. The anion B replaces another anion Y in a salt or an acid.
Examples:
2 NaCl(aq) + K2SO4(aq)  Na2SO4(aq) + 2KCl(aq)
2 AgNO3(aq) + ZnCl2(aq)  2AgCl(s) + Zn(NO3)2(aq)
3Ca(OH)2(aq) + 2H3PO4(aq)  Ca3(PO4)2(aq) +HOH(l)

12. 5. COMBUSTION REACTION Occurs when a substance combines with oxygen.
More commonly known as burning.

13. CH4(g) + 2 O2(g)  CO2(g) + 2 H2O(g)
Examples:
4 Fe(s) + 3 O2(g)  2 Fe2 O3 (s)
When compounds containing carbon and hydrogen undergo combustion with sufficient amount of oxygen, carbon dioxide and water are the products
Examples:
CH4(g) + 2 O2(g)  CO2(g) + 2 H2O(g)
2 C2H6(g) + 7 O2(g)  4 CO2(g) + 6 H2O(g)