Combination 2

 Absolutely, Mayank! Here's a student-friendly explanation of Activity 1.4 and the related discussion on Combination and Exothermic Reactions from NCERT Class 10 Science, written in a clear and engaging format for classroom teaching, revision notes, or worksheets.

🧪 Activity 1.4 – Reaction of Calcium Oxide with Water

(Related to Combination and Exothermic Reactions)

🎯 Aim:

To observe the reaction between quick lime (CaO) and water (H₂O) and identify the type of chemical reaction.

🧰 Materials Required:

  • Beaker

  • Calcium oxide (quick lime)

  • Water

  • Glass rod (optional)

🧪 Procedure:

  1. Take a small amount of calcium oxide (CaO) in a beaker.

  2. Slowly add water to it.

  3. Stir and touch the outside of the beaker gently.

👁️ Observation:

  • The mixture heats up noticeably.

  • The solution appears milky (suspension of slaked lime).

🔬 Explanation:

A chemical reaction occurs:

CaO (s)+H2O (l)→Ca(OH)2(aq)+Heat\text{CaO (s)} + \text{H}_2\text{O (l)} \rightarrow \text{Ca(OH)}_2 (aq) + \text{Heat}

  • CaO is quick lime

  • Ca(OH)₂ is slaked lime

  • Heat is released, so the beaker becomes warm

✅ This is a Combination Reaction and an Exothermic Reaction.

📘 Definition Recap:

🔹 Combination Reaction:

When two or more substances combine to form a single product, it's called a combination reaction.

🔹 Exothermic Reaction:

A reaction that releases heat along with product formation is called exothermic.

🔥 More Examples of Combination Reactions (from NCERT)

✅ (i) Burning of Coal

C (s)+O2(g)→CO2(g)\text{C (s)} + \text{O}_2 (g) \rightarrow \text{CO}_2 (g)

✅ (ii) Formation of Water

2H2(g)+O2(g)→2H2O(l)2\text{H}_2 (g) + \text{O}_2 (g) \rightarrow 2\text{H}_2\text{O} (l)

✅ (iii) Whitewashing Reaction

Over time, slaked lime reacts with CO₂ in air to form calcium carbonate, which gives a shiny white finish to walls:

Ca(OH)2(aq)+CO2(g)→CaCO3(s)+H2O(l)\text{Ca(OH)}_2 (aq) + \text{CO}_2 (g) \rightarrow \text{CaCO}_3 (s) + \text{H}_2\text{O} (l)

✅ CaCO₃ = white coating (also found in marble).

🌿 Real-Life Exothermic Reactions

Process Equation
Burning of natural gas CH4+2O2→CO2+2H2O+Heat\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O} + \text{Heat}
Respiration in cells C6H12O6+6O2→6CO2+6H2O+Energy\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{Energy}
Composting Vegetable waste → decomposes with heat release (biological exothermic)

📌 Concept Check:

Q: What type of reaction takes place in Activity 1.1 (burning of magnesium)?
A: It is both a combination reaction and an exothermic reaction, as it forms MgO with release of heat and light.

🎤 Final Thought for Class:

“Combination reactions help us build — from fuel to food to construction. When energy is released along the way, it keeps our world running!”

Would you like this reformatted as a flowchart, lab worksheet, or interactive quiz for your students?

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