RBSE Class 10 Science Chapter 1: Chemical Reactions and Equations (Complete Notes) 2026

From NCERT / RBSE Science • Exam Oriented • Updated for Board Exam 2026

Chemical Reactions and Equations (रासायनिक अभिक्रियाएँ एवं समीकरण) कक्षा 10 विज्ञान का प्रथम अध्याय है, जो आगे के सभी अध्यायों (Acids, Metals, Electricity आदि) की नींव रखता है। इस अध्याय से हर वर्ष बोर्ड परीक्षा में 6–10 अंक के प्रश्न पूछे जाते हैं।

What is a Chemical Reaction? (रासायनिक अभिक्रिया)

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

रासायनिक अभिक्रिया वह प्रक्रिया है जिसमें एक या अधिक पदार्थ आपस में क्रिया करके नए पदार्थ बनाते हैं जिनके गुण पहले से भिन्न होते हैं।

• रंग में परिवर्तन
• गैस का निकलना
• ताप का उत्सर्जन या अवशोषण
• अवक्षेप (Precipitate) का बनना

Chemical Equation (रासायनिक समीकरण)

A chemical equation represents a chemical reaction using symbols and formulas.

Magnesium + Oxygen → Magnesium Oxide
Mg + O₂ → MgO

Balanced and Unbalanced Equations

According to the Law of Conservation of Mass, mass can neither be created nor destroyed in a chemical reaction.

Unbalanced Equation:

Fe + H₂O → Fe₃O₄ + H₂

Balanced Equation:

3Fe + 4H₂O → Fe₃O₄ + 4H₂

Types of Chemical Reactions

1. Combination Reaction

Two or more substances combine to form a single product.

CaO + H₂O → Ca(OH)₂

2. Decomposition Reaction

A compound breaks down into two or more simpler substances.

CaCO₃ → CaO + CO₂

3. Displacement Reaction

A more reactive element displaces a less reactive element.

Zn + CuSO₄ → ZnSO₄ + Cu

4. Double Displacement Reaction

Exchange of ions between two compounds.

Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2NaCl

Oxidation and Reduction (Redox Reactions)

• Oxidation: Gain of oxygen / Loss of hydrogen
• Reduction: Loss of oxygen / Gain of hydrogen

Memory Trick (Exam Favourite):
OIL RIG → Oxidation Is Loss, Reduction Is Gain (of electrons)

Corrosion (संक्षारण)

Slow destruction of metals due to reaction with air and moisture is called corrosion.

Iron + Oxygen + Water → Rust

• Painting
• Galvanization
• Alloying

Rancidity (विकृतता)

Oxidation of fats and oils causing unpleasant smell and taste.

• Nitrogen packaging
• Refrigeration
• Use of antioxidants

Important Exam Questions

1. Define chemical reaction.
2. State law of conservation of mass.
3. Differentiate oxidation and reduction.
4. What is corrosion? How can it be prevented?
5. Explain displacement reaction with example.

MCQs (Board Pattern)

Q. Zn + CuSO₄ → ZnSO₄ + Cu is an example of:

• A. Combination
• B. Decomposition
• C. Displacement ✔
• D. Neutralization

Related Chapters: Acids Bases and Salts • Metals and Non-metals • Electricity • Magnetic Effects

© RBSE Class 10 Science Notes 2026 | Prepared for Board Examination