Chemical Reactions

A reaction occurs when two or more elements, mixtures, or compounds chemically combine to form new substances.

- Reactants: The starting materials.

- Products: The new substances formed.

Types of Reactions

1. Combination Reaction

2. Decomposition Reaction

3. Displacement Reaction

4. Double Decomposition Reaction

5. Catalytic Reaction

6. Reversible Reaction

7. Thermal Reaction

8. Oxidation/Reduction (Redox) Reaction

Combination Reaction

- Two or more substances combine to form a larger compound.

- Examples:

- Element + Element → Compound

- Compound + Compound → Bigger Compound

Decomposition Reaction

- A compound splits into two or more simpler substances when heat is applied.

- General form:

A --> B + C + D

Displacement Reaction

- An element displaces another element or radical in a compound.

- General form:

A + BY --> AY + B

- Rule: For displacement to occur, the displacing element must be higher in the electrochemical series than the displaced element.

Electrochemical Series

Positive Ions (Electropositivity order):

Gold < Silver < Copper < Hydrogen < Lead < Tin < Iron < Zinc < Aluminium < Magnesium < Calcium < Sodium < Potassium

Negative Ions (Electronegativity order):

Hydroxide < Iodide < Bromide < Chloride < Nitrate < Sulphate < Fluoride  

Double Decomposition

- Occurs when two soluble compounds (especially salts) react by exchanging their radicals.

- This forms two new salts:

- One is soluble,

- The other is either insoluble, volatile, or gaseous.

General Equation:

AB + CD --> AD + CB