science chapter 1 class 10

Class 10 Science – Chapter 1: Chemical Reactions and Equations – Notes



1. Introduction to Chemical Reactions

● A chemical reaction is a process in which one or more substances (reactants) are
converted into one or more new substances (products).
● Indicators of a chemical reaction:
○ Change in state
○ Change in colour
○ Evolution of gas
○ Change in temperature

2. Chemical Equations

● Representation of a chemical reaction using symbols and formulae.
● Example: Mg + O₂ → MgO
● Balanced Chemical Equation: Both sides of the equation have an equal number of
atoms of each element.

3. Types of Chemical Reactions

1. Combination Reaction
○ Two or more substances combine to form a new compound.
○ A + B → AB
○ Example: CaO + H₂O → Ca(OH)₂
2. Decomposition Reaction
○ A compound breaks down into two or more simpler substances.
○ AB → A + B
○ Example: 2H₂O → 2H₂ + O₂ (Electrolysis of water)
3. Displacement Reaction
○ A more reactive element displaces a less reactive element from its compound.
○ A + BC → AC + B
○ Example: Zn + CuSO₄ → ZnSO₄ + Cu
4. Double Displacement Reaction
○ Exchange of ions between two compounds.
○ AB + CD → AD + CB
○ Example: Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl
5. Oxidation and Reduction (Redox Reaction)
○ Oxidation: Gain of oxygen or loss of hydrogen.
○ Reduction: Loss of oxygen or gain of hydrogen.
○ Example: CuO + H₂ → Cu + H₂O

4. Effects of Oxidation Reactions