Chemical Reactions and Equations: Class 10 Notes

Have you ever wondered why milk turns sour when left outside, or why an iron nail gets rusty? Understanding chemical reactions is fundamental to the study of science. In Class 10, the chapter “Chemical Reactions and Equations” introduces students to the symbolic representation of chemical processes and explores how different substances interact to form new compounds. This chapter provides clarity on concepts like chemical equations, reaction types, oxidation, and how these principles apply to real-life situations. These NCERT science class 10 notes simplify the chapter concepts and help you score better in your exams.

📌 What is a Chemical Reaction?

A chemical reaction occurs when one or more substances (reactants) convert into new substances (products).

🔹How do we know a Chemical Reaction has occurred?

Change in state.
Change in color.
Evolution of gas.
Change in temperature (exothermic or endothermic).

These signs tell us that the original substance has changed its identity and new substances with different properties have formed.

📌 Chemical Equations: Word and Balanced Forms

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

Word Equation Example: Magnesium (solid) + Oxygen (gas) → Magnesium oxide (solid)

Chemical Equation: 2Mg + O₂ → 2MgO

A balanced chemical equation follows the Law of Conservation of Mass, where the number of atoms of each element is the same on both sides.

Example of a Balanced Equation: 3Fe + 4H₂O → Fe₃O₄ + 4H₂

📌 Steps to Balance a Chemical Equation

1st: Write the skeletal equation. 2nd: Count atoms on both sides. 3rd: Use coefficients to balance atoms. 4th: Check your work. 5th: Include state symbols: (s), (l), (g), (aq)

📌 Types of Chemical Reactions Explained

🔹A. Combination Reaction

Two or more reactants combine to form a single product. Example: CaO + H₂O → Ca(OH)₂

🔹B. Decomposition Reaction

A compound breaks down into two or more simpler substances. Example: CaCO₃ → CaO + CO₂

🔹C. Displacement Reaction

A more reactive element displaces a less reactive one from a compound. Example: Fe + CuSO₄ → FeSO₄ + Cu

🔹D. Double Displacement Reaction

Exchange of ions between two compounds forming new products. Example: Na₂SO₄ + BaCl₂ → BaSO₄ ↓ + 2NaCl

🔹E. Redox (Oxidation-Reduction) Reaction

Involves both oxidation and reduction. Example: CuO + H₂ → Cu + H₂O

📌 Energy Changes in Reactions

Exothermic: Releases heat (e.g., CH₄ + O₂ → CO₂ + 2H₂O + heat)
Endothermic: Absorbs heat (e.g., Photosynthesis: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂)

📌 Effects of Oxidation in Everyday Life

🔹Corrosion:

Slow deterioration of metals when exposed to moisture and air. Example: Rusting of iron (4Fe + 3O₂ + xH₂O → 2Fe₂O₃·xH₂O).

Damages buildings, bridges, cars, etc.

🔹Rancidity:

Oxidation of fats/oils

Causes bad smell and taste

Prevented by antioxidants, airtight packing, or flushing with nitrogen

Prevention methods:

Using airtight packaging
Adding antioxidants to food products
Storing in cool, dark places

Chemical reactions and equations class 10

📌 Important Equations and Examples

H₂ + Cl₂ → 2HCl
Zn + 2AgNO₃ → Zn(NO₃)₂ + 2Ag
2Al + 3CuCl₂ → 2AlCl₃ + 3Cu

📌 FAQs – Chemical Reactions and Equations Class 10

Q1. Why should we balance a chemical equation? A: We balance chemical equations to follow the Law of Conservation of Mass and accurately represent the actual quantities of substances involved in the reaction.

Q2. What is the difference between displacement and double displacement? A: Displacement reactions involve one element replacing another in a compound, while double displacement reactions involve an exchange of ions between two compounds to form two new compounds.

Q3. Give one example of an oxidation reaction in daily life. A: Rusting of iron is a common example of oxidation in daily life, where iron combines with oxygen and moisture to form iron oxide.