🧪 Chapter 1 – Chemical Reactions and Equations (Class 10 Chemistry)

 Welcome students! Here's your full, easy-to-understand Class 10 Science Chemistry Chapter 1 Notes – Chemical Reactions and Equations. Learn all the key points, examples, and practice questions in one place!

---

✅ What is a Chemical Reaction?

A chemical reaction is a process in which one or more substances (reactants) are converted into new substances (products) with different properties.

📌 Examples:

• Burning of coal:
  $C + O_2 \rightarrow CO_2$

• Rusting of iron:
  $Fe + O_2 + H_2O \rightarrow Fe_2O_3·xH_2O$

---

🧾 Chemical Equation

A chemical equation represents a chemical reaction using symbols and formulas.

🟢 Example:
$Zn + H_2SO_4 \rightarrow ZnSO_4 + H_2$

---

🔁 Balanced Chemical Equation

A balanced chemical equation has an equal number of atoms of each element on both sides.

🧮 Example:
$H_2 + Cl_2 \rightarrow 2HCl$ ✅ Balanced
$H_2 + O_2 \rightarrow H_2O$ ❌ Unbalanced
Balanced form:
$2H_2 + O_2 \rightarrow 2H_2O$ ✅

---

✏️ How to Balance Chemical Equations

Steps:

1. Write the unbalanced equation.

2. Count atoms on both sides.

3. Use coefficients to balance.

4. Double-check.

---

🔄 Types of Chemical Reactions

1. Combination Reaction

Two or more reactants combine to form a single product.
$A + B \rightarrow AB$
👉 Example:
$CaO + H_2O \rightarrow Ca(OH)_2$

---

2. Decomposition Reaction

One substance breaks into two or more products.
$AB \rightarrow A + B$
🌞 Types:

• Thermal (heat):
  $CaCO_3 \xrightarrow{heat} CaO + CO_2$

• Photolytic (light):
  $2AgCl \xrightarrow{sunlight} 2Ag + Cl_2$

• Electrolytic (electricity):
  $2H_2O \xrightarrow{electricity} 2H_2 + O_2$

---

3. Displacement Reaction

A more reactive element displaces a less reactive element.
$A + BC \rightarrow AC + B$
Example:
$Zn + CuSO_4 \rightarrow ZnSO_4 + Cu$

---

4. Double Displacement Reaction

Two compounds exchange ions.
$AB + CD \rightarrow AD + CB$
Example:
$Na_2SO_4 + BaCl_2 \rightarrow BaSO_4 \downarrow + 2NaCl$

---

5. Oxidation and Reduction (Redox Reactions)

• Oxidation: Gain of oxygen or loss of hydrogen.

• Reduction: Loss of oxygen or gain of hydrogen.

Example:
$CuO + H_2 \rightarrow Cu + H_2O$
Oxidation: H₂ → H₂O
Reduction: CuO → Cu

---

⚠️ Corrosion

The process of deterioration of metals due to reactions with air and moisture.
Example:
Rusting of iron
$Fe + O_2 + H_2O \rightarrow Fe_2O_3·xH_2O$

---

⚠️ Rancidity

Spoiling of food due to oxidation of fats and oils.
❌ It gives a bad taste and smell.
✅ Prevented by:

• Refrigeration

• Airtight containers

• Antioxidants

---

📘 Practice Questions

1. Balance the equation:
   $Fe + H_2O \rightarrow Fe_3O_4 + H_2$

2. Name the type of reaction:
   $Na + Cl_2 \rightarrow NaCl$

3. Why is photosynthesis not considered a decomposition reaction?

4. What is the difference between oxidation and reduction?

---

✅ Conclusion
Chemical reactions are everywhere! From rusting to digestion – understanding types, balancing, and effects helps us in everyday life and exams!