SII Logo
Back to Science (Class 10)
🔬Science (Class 10)

Chemical Reactions & Equations Class 10 Notes

Types of reactions, balancing equations, decomposition, displacement, and redox.

Class 10
Start Learning

Chemical Reactions & Equations — Detailed Notes

Chemical Reactions & Equations is an important chapter in Science (Class 10) and is frequently tested in both conceptual and application-based questions. Students should first understand the core definition, then connect the topic with real-life observations and exam patterns.

A chemical reaction involves the rearrangement of atoms in reactants to form new substances (products) with different properties. In school and entrance exams, questions usually check your conceptual clarity, step-wise logic, and ability to avoid common mistakes.

To prepare effectively, break Chemical Reactions & Equations into smaller sub-parts: definition, laws/rules, examples, formulas, and revision questions. After theory, solve short questions, then move to mixed-level numericals or application prompts.

A smart revision strategy is to maintain a one-page summary for Chemical Reactions & Equations. Include important terms, two solved examples, and last-minute checkpoints before exams.

Key Exam Points

  • Types: combination (A+B→AB), decomposition (AB→A+B), displacement, double displacement, oxidation-reduction (redox).
  • Balancing equations: law of conservation of mass — atoms of each element must be equal on both sides.
  • Oxidation: loss of electrons / gain of oxygen / loss of hydrogen. Reduction: gain of electrons / loss of oxygen / gain of hydrogen.
  • Exothermic reactions: release heat (combustion, respiration). Endothermic: absorb heat (photosynthesis, electrolysis).
  • Corrosion: slow oxidation of metals (rusting of iron: 4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃ → Fe₂O₃·xH₂O).
  • Rancidity: oxidation of fats/oils (prevented by antioxidants, vacuum packaging, nitrogen flushing).

Important Formula / Rule

Balanced equation example: 2H₂ + O₂ → 2H₂O | Fe₂O₃ + 2Al → Al₂O₃ + 2Fe (thermite)

What You Will Learn in Chemical Reactions & Equations

A chemical reaction involves the rearrangement of atoms in reactants to form new substances (products) with different properties.

  • Types: combination (A+B→AB), decomposition (AB→A+B), displacement, double displacement, oxidation-reduction (redox).
  • Balancing equations: law of conservation of mass — atoms of each element must be equal on both sides.
  • Oxidation: loss of electrons / gain of oxygen / loss of hydrogen. Reduction: gain of electrons / loss of oxygen / gain of hydrogen.
  • Exothermic reactions: release heat (combustion, respiration). Endothermic: absorb heat (photosynthesis, electrolysis).
  • Corrosion: slow oxidation of metals (rusting of iron: 4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃ → Fe₂O₃·xH₂O).
  • Rancidity: oxidation of fats/oils (prevented by antioxidants, vacuum packaging, nitrogen flushing).

Key Formulas

Balanced equation example: 2H₂ + O₂ → 2H₂OFe₂O₃ + 2Al → Al₂O₃ + 2Fe (thermite)

Example

Burning magnesium (2Mg + O₂ → 2MgO) is a combination reaction releasing bright white light.

Expected Exam Questions — Chemical Reactions & Equations

Q1.What is a redox reaction? Give an example.
Answer: A redox reaction involves simultaneous oxidation (electron loss) and reduction (electron gain). Example: CuO + H₂ → Cu + H₂O. CuO is reduced (O removed, gains H) to Cu; H₂ is oxidised (gains O) to H₂O. OIL RIG: Oxidation Is Loss, Reduction Is Gain (of electrons).
Q2.Differentiate between exothermic and endothermic reactions with examples.
Answer: Exothermic: heat is released (ΔH < 0). Examples: combustion (CH₄+O₂→CO₂+H₂O+heat), neutralisation (HCl+NaOH→NaCl+H₂O). Endothermic: heat is absorbed (ΔH > 0). Examples: photosynthesis (6CO₂+6H₂O+light→C₆H₁₂O₆+6O₂), decomposition of CaCO₃ on heating.
Q3.Why does iron corrode faster in salt water?
Answer: Salt water (NaCl solution) is a better electrolyte than pure water, increasing the rate of electrochemical reactions that cause rusting. Chloride ions (Cl⁻) remove the protective oxide layer and accelerate oxidation.

🔘 MCQ Practice — Chemical Reactions & Equations

MCQ 1.Which of the following is a decomposition reaction?
A. 2H₂+O₂→2H₂O
B. 2KClO₃→2KCl+3O₂ ✓
C. Fe+S→FeS
D. NaOH+HCl→NaCl+H₂O

✓ Correct Answer: 2KClO₃→2KCl+3O₂

Download Chemical Reactions & Equations PDF Notes

Get the complete Chemical Reactions & Equations notes as a PDF — free for enrolled students, or browse our public study materials library.

Browse & DownloadEnroll for Full Access

More Science (Class 10) Topics

Acids, Bases & SaltsMetals & Non-MetalsCarbon & its CompoundsLife ProcessesControl & CoordinationReproduction in OrganismsHeredity & EvolutionLight — Reflection & Refraction
View All Science (Class 10) Topics →

Related Subjects

📘

Artificial Intelligence and Machine Learning

All Levels

⚛️

Physics

Class 11

🧪

Chemistry

Class 11

📐

Mathematics

Class 10

🧬

Biology

Class 11

💻

Computer Science

Class 11

🖥️

Informatics Practices

Class 11

☕

Java Programming

Beginner

Browse All Subjects →

Latest Updates

View all

2026-04-20

CBSE Board Exam Update 2026

CBSE announced competency-focused question weightage updates for Class 10 and 12 board papers.

2026-02-28

CBSE Practical Submission Circular 2026

Schools received updated practical record submission windows for board-affiliated science streams.

Frequently Asked Questions — Chemical Reactions & Equations

What is Chemical Reactions & Equations in Science (Class 10)?
A chemical reaction involves the rearrangement of atoms in reactants to form new substances (products) with different properties.
What is a redox reaction? Give an example.
A redox reaction involves simultaneous oxidation (electron loss) and reduction (electron gain). Example: CuO + H₂ → Cu + H₂O. CuO is reduced (O removed, gains H) to Cu; H₂ is oxidised (gains O) to H₂O. OIL RIG: Oxidation Is Loss, Reduction Is Gain (of electrons).
Differentiate between exothermic and endothermic reactions with examples.
Exothermic: heat is released (ΔH < 0). Examples: combustion (CH₄+O₂→CO₂+H₂O+heat), neutralisation (HCl+NaOH→NaCl+H₂O). Endothermic: heat is absorbed (ΔH > 0). Examples: photosynthesis (6CO₂+6H₂O+light→C₆H₁₂O₆+6O₂), decomposition of CaCO₃ on heating.
Why does iron corrode faster in salt water?
Salt water (NaCl solution) is a better electrolyte than pure water, increasing the rate of electrochemical reactions that cause rusting. Chloride ions (Cl⁻) remove the protective oxide layer and accelerate oxidation.
How do I prepare Chemical Reactions & Equations for exams?
To master Chemical Reactions & Equations, start by reading the theory carefully, then go through solved examples step by step. Practice numericals (if applicable), revise key formulas, and attempt previous year questions. SII notes cover all these aspects in a structured manner.
Are these Chemical Reactions & Equations notes free?
Yes! SII provides free access to Chemical Reactions & Equations notes and introductory study materials. Enrolled students get full access to detailed notes, solved papers, and live doubt-clearing sessions.
Which exams ask questions from Chemical Reactions & Equations?
Chemical Reactions & Equations is an important topic tested in Class 10 board exams, as well as CBSE Class 10 Boards, ICSE Class 10. It frequently appears in both short-answer and long-answer sections.