exothermic 2

 Here’s a complete, CBSE Class 10–oriented explanation of Endothermic Reactions, written in a clear, engaging, and exam-friendly format — perfect for classroom teaching, revision notes, or student handouts.

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❄️ Endothermic Reactions

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

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🎯 Definition:

An endothermic reaction is a chemical reaction that absorbs energy (usually in the form of heat) from the surroundings.

✅ As a result, the temperature of the surroundings decreases.

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📘 Key Characteristics:

• Reactants absorb energy to form products.

• Usually requires a continuous supply of energy.

• Often feels cold to touch.

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🔥 Examples of Endothermic Reactions

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✅ 1. Thermal Decomposition of Calcium Carbonate

$$\text{CaCO}_3 (s) \xrightarrow{\text{Heat}} \text{CaO} (s) + \text{CO}_2 (g)$$

• Heat is required to break CaCO₃ into CaO and CO₂.

• Used in cement industries.

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✅ 2. Electrolysis of Water (Electrolytic Decomposition)

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

• Electric energy is absorbed to split water into hydrogen and oxygen.

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✅ 3. Photolytic Decomposition of Silver Chloride

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

• Light energy is absorbed to decompose AgCl.

• Used in photography.

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✅ 4. Barium Hydroxide + Ammonium Chloride Reaction

$$\text{Ba(OH)}_2 + 2\text{NH}_4\text{Cl} \rightarrow \text{BaCl}_2 + 2\text{NH}_3 + 2\text{H}_2\text{O}$$

• The test tube becomes cold as the reaction absorbs heat.

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🔍 Comparison: Endothermic vs. Exothermic

Endothermic	Exothermic
Absorbs heat	Releases heat
Surroundings become cold	Surroundings become warm
Common in decomposition reactions	Common in combustion, respiration, etc.

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🧠 Exam Tip (CBSE Pattern):

Q: Give one example each of endothermic and exothermic reactions with balanced equations.
✅ Answer:

• Endothermic:

  $$\text{CaCO}_3 \xrightarrow{\text{Heat}} \text{CaO} + \text{CO}_2$$

• Exothermic:

  $$\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O} + \text{Heat}$$

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🎤 Closing Line for Students:

“Endothermic reactions are like chemical coolers — they pull energy in and quietly change the substance inside.”

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Would you like a concept map, matching worksheet, or digital quiz to help your students practice endothermic vs. exothermic reactions?