decomposition reaction

 Certainly, Mayank! Here's a complete, student-friendly explanation of the Decomposition Reaction (as per NCERT Class 10 Chapter 1 – Chemical Reactions and Equations), perfect for classroom teaching, student notes, or revision.

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💥 1.2.2 Decomposition Reaction

(Class 10 – CBSE Science)

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🎯 What is a Decomposition Reaction?

A decomposition reaction is a type of chemical reaction in which a single compound breaks down into two or more simpler substances (elements or compounds).

📘 General Form:

$$AB \rightarrow A + B$$

✅ Opposite of a Combination Reaction.

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🔥 Types of Decomposition Reactions

Decomposition can occur due to:

1. Heat → Thermal Decomposition

2. Light → Photolytic Decomposition

3. Electricity → Electrolytic Decomposition

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🧪 1. Thermal Decomposition

(Breaking down by heating)

Example:

$$2\text{Pb(NO}_3)_2 \xrightarrow{\text{heat}} 2\text{PbO} + 4\text{NO}_2 + \text{O}_2$$

✅ Lead nitrate breaks down on heating to form:

• Lead oxide (PbO)

• Nitrogen dioxide (NO₂) → brown gas

• Oxygen (O₂)

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🧪 2. Photolytic Decomposition

(Breaking down by light)

Example:

$$2\text{AgCl} \xrightarrow{\text{sunlight}} 2\text{Ag} + \text{Cl}_2$$

✅ Silver chloride breaks down in sunlight to form:

• Silver (Ag) (grey coating)

• Chlorine gas (Cl₂)

📌 Important Note:
This is why silver chloride is stored in dark bottles.

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🧪 3. Electrolytic Decomposition

(Using electricity to break down compounds)

Example (Activity 1.7 – Electrolysis of water):

$$2\text{H}_2\text{O (l)} \xrightarrow{\text{electricity}} 2\text{H}_2 (g) + \text{O}_2 (g)$$

✅ Water splits into:

• Hydrogen gas (H₂) (collected in double amount)

• Oxygen gas (O₂)

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💡 Common Features of Decomposition Reactions:

• One reactant → Two or more products

• Often need energy input (heat, light, or electricity)

• Can be used to extract elements from compounds

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🧠 Exam Tip (CBSE Style):

Question Type	Expected Answer
Define decomposition reaction	A reaction where a compound breaks into simpler substances
Write an example of photolytic decomposition	$2\text{AgBr} \xrightarrow{\text{sunlight}} 2\text{Ag} + \text{Br}_2$
What type of reaction is 2H₂O → 2H₂ + O₂?	Electrolytic Decomposition

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📖 Daily Life Application:

• Photosynthesis (indirect): Light drives complex reactions

• Chlorine preparation using electrolysis

• Bleaching powders use decomposition of chlorine compounds

• Photography: Decomposition of AgCl helps form images on photo paper

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🎤 Final Thought for Students:

“Decomposition is chemistry's way of breaking down the old to prepare for the new — powered by heat, light, or electricity!”

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Would you like a worksheet, animation link, or quiz to reinforce decomposition reaction types for your students?