decomposition 2

 Absolutely, Mayank! Here's a comprehensive, CBSE Class 10–style explanation of Activity 1.5 to Activity 1.8, all related to the Decomposition Reaction, including thermal, electrolytic, and photolytic types, with observations, equations, types of energy involved, and a practical closing activity.

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💥 1.2.2 Decomposition Reactions

(Class 10 Science – Chapter 1: Chemical Reactions and Equations)

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🧠 Definition:

A decomposition reaction is a reaction in which a single compound breaks down into two or more simpler substances when energy is supplied.

📘 General Form:

$$AB \rightarrow A + B$$

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📌 Types of Decomposition Reactions:

Type	Energy Source
Thermal	Heat
Electrolytic	Electricity
Photolytic	Light

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🔥 Activity 1.5 – Thermal Decomposition of Ferrous Sulphate

✅ Observation:

• Green crystals turn brown when heated.

• A suffocating smell of burning sulphur is noticed.

🧪 Chemical Reaction:

$$2\text{FeSO}_4 (s) \xrightarrow{\text{Heat}} \text{Fe}_2\text{O}_3 (s) + \text{SO}_2 (g) + \text{SO}_3 (g)$$

• Ferrous sulphate decomposes into:

  • Ferric oxide (Fe₂O₃) → brown solid

  • Sulphur dioxide (SO₂) and sulphur trioxide (SO₃) → gases

✅ Type: Thermal decomposition

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🔥 Activity 1.6 – Thermal Decomposition of Lead Nitrate

✅ Observation:

• White lead nitrate turns yellowish brown.

• Brown fumes (NO₂ gas) are seen.

🧪 Chemical Reaction:

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

✅ Type: Thermal decomposition
✅ Gas evolved: Nitrogen dioxide (NO₂)

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⚡ Activity 1.7 – Electrolytic Decomposition of Water

✅ Observation:

• Gas bubbles at both electrodes.

• Hydrogen is collected at the cathode and oxygen at the anode.

• Volume of hydrogen is double that of oxygen.

🧪 Chemical Reaction:

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

✅ Type: Electrolytic decomposition
✅ Testing Gases:

• Hydrogen: Burns with a pop sound

• Oxygen: Relights a glowing splint

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🌞 Activity 1.8 – Photolytic Decomposition of Silver Salts

✅ Observation:

• White AgCl turns grey in sunlight.

• Grey colour is due to silver metal formation.

🧪 Reactions:

$$2\text{AgCl} (s) \xrightarrow{\text{Sunlight}} 2\text{Ag} (s) + \text{Cl}_2 (g)$$ $$2\text{AgBr} (s) \xrightarrow{\text{Sunlight}} 2\text{Ag} (s) + \text{Br}_2 (g)$$

✅ Type: Photolytic decomposition
✅ Use: Black-and-white photography

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🧊 Bonus Activity: Barium Hydroxide + Ammonium Chloride

✅ Observation:

• Mixture becomes cold.

• It absorbs heat from surroundings.

🧪 Reaction Type:

Endothermic Reaction (absorbs heat)

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📚 Important Notes for CBSE Students:

📘 Decomposition vs Combination:

Combination Reaction	Decomposition Reaction
Two or more reactants → One product	One compound → Two or more products
Often exothermic	Often endothermic
E.g., CaO + H₂O → Ca(OH)₂	CaCO₃ → CaO + CO₂

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🎓 Final Thought:

“Decomposition reactions are nature's way of breaking complex things into simpler parts — from industrial chemicals to digital photos.”

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Would you like a revision worksheet, flashcard set, or interactive activity sheet for all three decomposition types (thermal, electrolytic, photolytic)?