1. Types of Chemical Reactions

2. Synthesis Type 1: SYNTHESIS
Definition: Two or more reactants combine to form one product
Key sign: One product
General Structure: A + X  AX
Examples:
CO + O2  CO3
2Mg + O2  2MgO

3. Decomposition Type 2: DECOMPOSITION
Definition: One reactant breaks down into two or more products
Key sign: One reactant
General Structure: AX  A + X
Examples:
H2CO3  CO2 + H2O
NCl3  N2 + Cl2

4. Single Replacement (Displacement)
Type 3: SINGLE REPLACEMENT (OR DISPLACEMENT)
Definition: A single element replaces another element in a compound
Key sign: One single element and a compound on both sides of the equation
General Structure: A + BX  AX + B
Examples:
H2SO4 + Ca  CaSO4 + H2
Li + H2O  LiOH + H2

5. Double Replacement (Displacement)
Type 4: DOUBLE REPLACEMENT (OR DISPLACEMENT)
Definition: Two ions replace each other to form two different compounds
Key sign: Two compounds on both sides of the equation
General Structure: AX + BY  AY + BX
Examples:
CaCl2 + K3PO4  Ca3(PO4)2 + KCl
Al2(SO4)3 + Ca(OH)2  Al(OH)3 + CaSO4
Special type of double replacement reaction is an acid-base reaction. An acid reacts with a base and the products are always a salt and water (H2O).

6. Combustion Type 5: COMBUSTION
Definition: A chemical burns in oxygen to produce light/heat
Key sign: Oxygen is a reactant, carbon dioxide and water are products (or vice versa)
General Structure: A + O2  CO2 + H2O
Examples:
C10H22 + O2  CO2 + H2O
CH4 + O2  CO2 + H2O

7. Questions to Ask…
Does the reaction have oxygen as one of the reactants and carbon dioxide and water as products? If yes, then combustion.
Does your reaction have two or more chemicals combining to form one chemical? If yes, then synthesis.
Does your reaction have one molecule falling apart to create several small ones? If yes, then decomposition.
Does your reaction have any molecules that are only one element? If yes, then single displacement.
Does your reaction have two molecules that switch partners? If yes, then double displacement.