Chemical Reactions and Equations

Notes

1. Chapter Revision (Quick Revision)

Chemical Reaction

A process in which one or more substances change into new substances having different properties is called a chemical reaction.

Indicators of Chemical Reaction

Change in colour

Evolution of gas

Change in temperature

Formation of precipitate

Change in state

Example:

2Mg+O

2

​

→2MgO

Magnesium burns with a bright white flame and forms magnesium oxide.

2. Chemical Equations

Word Equation

Magnesium + Oxygen → Magnesium Oxide

Skeletal Equation

Mg + O₂ → MgO

Balanced Equation

2Mg+O

2

​

→2MgO

Balancing is done according to the Law of Conservation of Mass.

3. Types of Chemical Reactions

A. Combination Reaction

Two or more substances combine to form a single product.

General form:

A + B → AB

Example:

CaO+H

2

​

O→Ca(OH)

2

​

+Heat

Quicklime + Water → Slaked lime

B. Decomposition Reaction

One compound breaks into simpler substances.

General form:

AB → A + B

(i) Thermal Decomposition

CaCO

3

​

Heat

​

CaO+CO

2

​

(ii) Electrolytic Decomposition

2H

2

​

O

Electricity

​

2H

2

​

+O

2

​

(iii) Photolytic Decomposition

2AgCl

Sunlight

​

2Ag+Cl

2

​

C. Displacement Reaction

A more reactive element displaces a less reactive element.

General form:

A + BC → AC + B

Example:

Zn+CuSO

4

​

→ZnSO

4

​

+Cu

D. Double Displacement Reaction

Exchange of ions between two compounds.

Example:

BaCl

2

​

+Na

2

​

SO

4

​

→BaSO

4

​

+2NaCl

White precipitate of BaSO₄ is formed.

E. Precipitation Reaction

Formation of an insoluble substance.

Example:

BaCl₂ + Na₂SO₄ → BaSO₄↓

F. Oxidation and Reduction

Oxidation

Addition of oxygen or removal of hydrogen.

Example:

2Cu+O

2

​

→2CuO

Reduction

Removal of oxygen or addition of hydrogen.

Example:

CuO+H

2

​

→Cu+H

2

​

O

Redox Reaction

Oxidation and reduction occur simultaneously.

Example:

CuO+H

2

​

→Cu+H

2

​

O

4. Exothermic and Endothermic Reactions

Exothermic Reaction

Heat is released.

Example:

…