Chemical Reactions and Equations — Science Class 10 Notes (CBSE & HBSE)
Free NCERT Science notes for Chemical Reactions and Equations (Class 10) on Siksha Sarovar, aligned to CBSE and Haryana Board (HBSE). This chapter is broken into 3 topics with clear explanations, formulas, solved examples and board-pattern practice — free to read, no sign-up required.
Board exam focus — Chemical Reactions and Equations (CBSE & HBSE)
Focuses on identifying chemical changes, balancing equations, and understanding various reaction types. CBSE emphasizes observation-based questions; HBSE focuses on direct definitions and balancing.
Writing and Balancing Chemical Equations
A chemical equation represents a chemical reaction using symbols and formulas of the substances involved.
Why Balance Equations?
According to the Law of Conservation of Mass, matter can neither be created nor destroyed in a chemical reaction. Therefore, the total mass of elements present in the products must be equal to the total mass of elements in the reactants.
Balancing Status Table
| Element | Reactants (LHS) | Products (RHS) | Balanced? |
|---|---|---|---|
| Iron (Fe) | 1 | 3 | No |
| Hydrogen (H) | 2 | 2 | Yes |
| Oxygen (O) | 1 | 4 | No |
Steps to Balance (Hit and Trial Method):
- Write the word equation and then symbols.
- Count the number of atoms of each element on both sides.
- Balance elements one by one, starting with the one that has the maximum number of atoms.
- Ensure all elements are balanced and write the physical states (s, l, g, aq).
Diagram Indicator: [Illustration of a balance scale with reactants on one side and products on the other, showing equal number of atoms after balancing.]
Types of Chemical Reactions
Chemical reactions involve the breaking and making of bonds between atoms to produce new substances.
1. Combination Reaction
Two or more reactants combine to form a single product.
- General form: A + B → AB
- Example: CaO(s) + H₂O(l) → Ca(OH)₂(aq) (Slaking of lime)
2. Decomposition Reaction
A single reactant breaks down to give simpler products. Requires energy (heat, light, or electricity).
- Thermal Decomposition: CaCO₃(s) + Heat → CaO(s) + CO₂(g)
- Electrolytic Decomposition: 2H₂O(l) + Electricity → 2H₂(g) + O₂(g)
- Photolytic Decomposition: 2AgCl(s) + Sunlight → 2Ag(s) + Cl₂(g)
3. Displacement Reaction
A more reactive element displaces a less reactive element from its compound.
- Example: Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s) (Iron displaces Copper)
Double Displacement, Oxidation & Reduction
4. Double Displacement Reaction
Exchange of ions between reactants to form new compounds. Often results in a precipitate.
- Example: Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq)
5. Oxidation and Reduction (Redox)
- Oxidation: Gain of oxygen or loss of hydrogen.
- Reduction: Loss of oxygen or gain of hydrogen.
- Redox Reaction: When oxidation and reduction occur simultaneously.
- Example: CuO + H₂ + Heat → Cu + H₂O
- CuO is reduced to Cu (loss of oxygen).
- H₂ is oxidized to H₂O (gain of oxygen).
Frequently asked questions
Are these Chemical Reactions and Equations notes free?
Yes — the Chemical Reactions and Equations notes for Science (Class 10) on Siksha Sarovar are completely free to read, with no account required.
Do these notes follow CBSE and HBSE?
Yes. The Chemical Reactions and Equations notes are NCERT-aligned and include guidance for both CBSE and Haryana Board (HBSE), with important questions and MCQs for revision.
What does the Chemical Reactions and Equations chapter cover?
Concept explanations, key formulas and definitions, fully solved examples and board-pattern practice questions for Chemical Reactions and Equations.