Chapter 1 – Chemical Reactions and Equations (SSLC Karnataka 2024–25)
🧪 Lesson 1 – Chemical Reactions and Equations
(Easy Student Notes – Karnataka SSLC Pattern 2024–25)
🌿 1. What is a Chemical Reaction?
When two or more substances react to form new substances, the process is called a chemical reaction.
Example:
Magnesium + Oxygen → Magnesium Oxide
(Mg + O₂ → 2MgO)
🗣️ Kannada: ಎರಡು ಅಥವಾ ಹೆಚ್ಚು ಪದಾರ್ಥಗಳು ಸೇರಿ ಹೊಸ ಪದಾರ್ಥ ರಚಿಸಿದರೆ ಅದನ್ನು ರಾಸಾಯನಿಕ ಕ್ರಿಯೆ ಎನ್ನುತ್ತಾರೆ.
🧾 2. What is a Chemical Equation?
A short way of writing a chemical reaction using symbols and formulae of the substances.
Example:
Word Equation → Magnesium + Oxygen → Magnesium oxide
Chemical Equation → 2Mg + O₂ → 2MgO
🗣️ Kannada: ರಾಸಾಯನಿಕ ಕ್ರಿಯೆಯನ್ನು ಚಿಹ್ನೆಗಳ ಮೂಲಕ ತೋರಿಸಿದರೆ ಅದನ್ನು ರಾಸಾಯನಿಕ ಸಮೀಕರಣ ಎನ್ನುತ್ತಾರೆ.
⚖️ 3. Why Do We Balance Chemical Equations?
Because the Law of Conservation of Mass says:
👉 “Mass can neither be created nor destroyed.”
So, number of atoms on both sides must be equal.
💡 Balancing Equations – Easy Tricks
| Tip | Explanation | Example |
|---|---|---|
| 🔹 Step 1 | Write correct formulas | Fe + H₂O → Fe₃O₄ + H₂ |
| 🔹 Step 2 | Count atoms on both sides | Fe (1 & 3), O (1 & 4), H (2 & 2) |
| 🔹 Step 3 | Balance metals first | 3Fe + 4H₂O → Fe₃O₄ + 4H₂ |
| 🔹 Step 4 | Balance oxygen & hydrogen next |
Use even numbers |
| 🔹 Step 5 | Check again! Same number of atoms on both sides |
✅ Short Trick Words:
M – NM – O – H (Metal → Nonmetal → Oxygen → Hydrogen)
✅ Common Fractions Tip:
If you get ½ O₂, multiply the whole equation by 2.
✅ Practice Balancing Examples:
-
H₂ + Cl₂ → 2HCl
-
2Mg + O₂ → 2MgO
-
CaCO₃ → CaO + CO₂
-
Fe + CuSO₄ → FeSO₄ + Cu
-
2Na + 2H₂O → 2NaOH + H₂
🔄 4. Types of Chemical Reactions
| Type | Explanation | Example | |
|---|---|---|---|
| Combination |
Two or more → one |
A + B → AB (Mg + O₂ → MgO) | |
| Decomposition |
One → many |
AB → A + B (CaCO₃ → CaO + CO₂) |
|
| Displacement |
One replaces another |
Zn + CuSO₄ → ZnSO₄ + Cu |
|
| Double Displacement |
Exchange of ions |
BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl |
|
| Redox | Both oxidation + reduction |
CuO + H₂ → Cu + H₂O |
🌡️ 5. Exothermic and Endothermic Reactions
| Type | Meaning | Example |
|---|---|---|
| Exothermic |
Heat is released |
C + O₂ → CO₂ + Heat |
| Endothermic | Heat is absorbed | 2AgCl → 2Ag + Cl₂ (in sunlight) |
🧠 Memory tip:
➡️ Exo = Exit heat
➡️ Endo = Enters heat
⚙️ 6. Oxidation and Reduction
| Type | Definition | Example |
|---|---|---|
| Oxidation |
Gain of oxygen or loss of hydrogen |
Cu → CuO |
| Reduction |
Loss of oxygen or gain of hydrogen |
CuO → Cu |
| Redox Reaction | Both oxidation & reduction in same reaction |
CuO + H₂ → Cu + H₂O |
🗣️ Kannada:
ಆಕ್ಸೀಕರಣ = ಆಮ್ಲಜನಕ ಸೇರುವುದು
ಆಪಚಯ = ಆಮ್ಲಜನಕ ಕಳೆದುಹೋಗುವುದು
🌍 7. Effects of Oxidation in Daily Life
| Example | Type | Prevention |
|---|---|---|
| Rusting of Iron |
Oxidation | Apply paint, oil, or galvanize |
| Rancidity of Food (bad smell) |
Oxidation | Airtight container, fridge |
| Tarnishing of Silver | Oxidation | Polish it, keep covered |
🗣️ Kannada: ಕಬ್ಬಿಣದ ತುಕ್ಕು – ಆಕ್ಸೀಕರಣದ ಉತ್ತಮ ಉದಾಹರಣೆ.
🧠 8. Extra Important Exam Questions
🔹 1 Mark Questions
-
What is a chemical reaction?
-
What is a chemical equation?
-
Why do we balance a chemical equation?
-
Define oxidation and reduction.
-
Give one example for a double displacement reaction.
-
Name the reaction: CaCO₃ → CaO + CO₂
-
What is corrosion?
-
What is rancidity?
-
Why are chip packets filled with nitrogen gas?
-
Write an example of an exothermic reaction.
🔹 2 Mark Questions
-
Write any two observations that show a chemical reaction has occurred.
-
What are endothermic and exothermic reactions? Give one example each.
-
Explain redox reaction with example.
-
How can rusting of iron be prevented?
-
Balance and name the following:
a) Na + H₂O → NaOH + H₂
b) H₂ + Cl₂ → HCl
🔹 3 Mark Questions
-
What are the different types of chemical reactions? Explain with examples.
-
Write balanced equations for:
a) Electrolysis of water
b) Reaction of zinc with HCl
c) Reaction of calcium carbonate on heating -
What are oxidation and reduction? Explain with one experiment.
🔹 4 Mark Questions
-
When lead nitrate reacts with potassium iodide,
a) Write the balanced equation.
b) Name and color of precipitate formed.
c) Identify the type of reaction.
Answer:
Pb(NO₃)₂ + 2KI → 2KNO₃ + PbI₂ (yellow ppt.) → Double Displacement. -
Explain any four types of chemical reactions with balanced equations.
🪄 Extra Balancing Practice Set
Try to balance the following:
-
Fe + H₂O → Fe₃O₄ + H₂
-
Al + HCl → AlCl₃ + H₂
-
H₂ + O₂ → H₂O
-
C₂H₆ + O₂ → CO₂ + H₂O
-
Na₂CO₃ + HCl → NaCl + CO₂ + H₂O
🧩 Quick Recap Table
| Concept | Key Point | Example |
|---|---|---|
| Combination |
2 or more → 1 | H₂ + Cl₂ → 2HCl |
| Decomposition |
1 → 2 or more | CaCO₃ → CaO + CO₂ |
| Displacement |
One replaces another | Fe + CuSO₄ → FeSO₄ + Cu |
| Double Displacement |
Ion exchange | Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl |
| Redox | Oxidation & Reduction together |
CuO + H₂ → Cu + H₂O |
📘 Smart Study Tips
✅ Study balanced equations daily — 5 mins practice every day.
✅ Draw arrows to show which atom increases/decreases in balancing.
✅ Make a chart of types of reactions and paste near your study table.
✅ Before the exam, revise definitions (Chemical equation, oxidation, corrosion, rancidity).
✅ Write examples neatly — these fetch easy marks!
🏫 Need help with practice or doubt-solving?
Visit Skillset Tutorials, Akhtar Raza Circle, Davanagere — they give special SSLC practice on Balancing Equations & Reaction Types with experiments and model question papers.
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