Class 10 Chemical Reactions and Equations

🔹 1. What is a Chemical Reaction?

A chemical reaction is a process where one or more substances (reactants) are transformed into new substances (products) with different properties.

🔍 Key Indicators:

• Change in state
• Change in color
• Evolution of gas
• Change in temperature (heat released or absorbed)
• Formation of precipitate

Example:
Burning magnesium:
Mg + O₂ → MgO

 

🔹 2. Chemical Equations

Word Equation
Hydrogen + Oxygen → Water

Skeletal Equation
H₂ + O₂ → H₂O

Balanced Equation
2H₂ + O₂ → 2H₂O

Law of Conservation of Mass
“Mass is neither created nor destroyed in a chemical reaction.”

Balancing Equations is essential to obey this law.

 

🔹 3. Types of Chemical Reactions

Type	Explanation	Example
Combination	Two or more reactants → one product	CaO + H₂O → Ca(OH)₂
Decomposition	One reactant → two/more products	Pb(NO₃)₂ → PbO + NO₂ + O₂ (heat)
Displacement	A reactive element displaces another	Zn + CuSO₄ → ZnSO₄ + Cu
Double Displacement	Ions exchanged; forms precipitate/gas	Na₂SO₄ + BaCl₂ → BaSO₄↓ + NaCl
Redox	Simultaneous oxidation and reduction	CuO + H₂ → Cu + H₂O

 

🔹 4. Redox Reaction

• Oxidation: Gain of O₂ / Loss of electrons / Loss of H
• Reduction: Loss of O₂ / Gain of electrons / Gain of H

Example:
CuO + H₂ → Cu + H₂O
CuO is reduced, H₂ is oxidized.

 

🔹 5. Effects of Oxidation in Daily Life

Corrosion:

Slow oxidation of metals in presence of air/moisture.
Example: Rusting of iron
4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃
→ Affects bridges, vehicles, pipelines (economic loss)

Rancidity:

Oxidation of oils/fats → bad smell/taste
→ Prevention: Refrigeration, Antioxidants, Nitrogen packing

 

🔹 6. Important Examples (From NCERT)

1. Mg + O₂ → MgO
2. Zn + H₂SO₄ → ZnSO₄ + H₂
3. Fe + CuSO₄ → FeSO₄ + Cu
4. Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2NaCl
5. CaCO₃ → CaO + CO₂

 

🔹 7. Concept Map (Quick Revision)

Chemical Reaction
│
├── Indicators (gas, heat, color, ppt)
├── Types
│ ├── Combination
│ ├── Decomposition (heat/light/electricity)
│ ├── Displacement
│ ├── Double Displacement
│ └── Redox
├── Law: Conservation of Mass
├── Effects: Corrosion, Rancidity
└── Real-life relevance (industry, environment)

Read – Summary Notes