Types of Chemical Reactions Summary Notes: Class 10 NCERT Science

Chemical reactions are happening all around us, from the rusting of iron to the digestion of food in our bodies. While there are countless chemical reactions in nature, scientists have organized them into distinct categories based on their patterns and characteristics. These types of chemical reactions provide a framework for understanding and predicting how substances interact with each other.

In this learning resource, we’ll explore the fascinating world of chemical reaction types. You’ll discover how some reactions bring substances together to form new compounds, while others break substances apart. Some reactions involve elements trading places, and others feature a swap of components between compounds.

Understanding these types of chemical reactions is like learning the basic vocabulary of chemistry. Once you recognize these patterns, you’ll be able to predict what happens when substances interact, making chemistry much more intuitive and less about memorization.

Each reaction type follows specific rules and shows particular signs that help us identify and classify them. By learning these categories – combination, decomposition, displacement, and double displacement reactions – you’ll understand the chemical changes that shape our world.

NCERT Science Textbook, Class 10, Chapter 1: Chemical Reactions and Equations

1. Combination Reactions

• Definition: Two or more substances combine to form a single product
• General equation: A + B → AB
• Key characteristics:
  • Often exothermic (release energy)
  • Can involve elements combining with each other or with compounds
• Examples:
  • Calcium oxide + Water → Calcium hydroxide: CaO(s) + H₂O(l) → Ca(OH)₂(aq) + heat
  • Carbon + Oxygen → Carbon dioxide: C(s) + O₂(g) → CO₂(g)
  • Magnesium + Oxygen → Magnesium oxide: 2Mg(s) + O₂(g) → 2MgO(s)
• Combination Reactions (Section 1.2.1) – With examples like calcium oxide reacting with water, burning of coal, and formation of water from hydrogen and oxygen.

2. Decomposition Reactions

• Definition: A single compound breaks down into two or more simpler substances
• General equation: AB → A + B
• Key characteristics:
  • Usually require energy input (endothermic)
  • Energy can be supplied as heat, light, or electricity
• Types of decomposition:
  • Thermal decomposition (requires heat)
  • Electrolytic decomposition (requires electricity)
  • Photochemical decomposition (requires light)
• Examples:
  • Calcium carbonate → Calcium oxide + Carbon dioxide: CaCO₃(s) → CaO(s) + CO₂(g)
  • Water → Hydrogen + Oxygen (electrolysis): 2H₂O(l) → 2H₂(g) + O₂(g)
  • Silver chloride → Silver + Chlorine (photodecomposition): 2AgCl(s) → 2Ag(s) + Cl₂(g)
• Decomposition Reactions (Section 1.2.2) – Including thermal decomposition examples like ferrous sulphate, calcium carbonate, lead nitrate, and other types like electrolytic decomposition of water and photochemical decomposition of silver chloride/bromide.

3. Displacement Reactions (Single Replacement)

• Definition: A more reactive element displaces a less reactive element from its compound
• General equation: A + BC → AC + B
• Key characteristics:
  • Reactivity determines if displacement will occur
  • Common in metal-acid reactions
• Examples:
  • Zinc + Copper sulfate → Zinc sulfate + Copper: Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)
  • Iron + Copper chloride → Iron chloride + Copper: Fe(s) + CuCl₂(aq) → FeCl₂(aq) + Cu(s)
  • Zinc + Hydrochloric acid → Zinc chloride + Hydrogen: Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)
• Displacement Reactions (Section 1.2.3) – With examples like iron displacing copper from copper sulphate, zinc displacing copper, and lead displacing copper.

4. Double Displacement Reactions

• Definition: Exchange of ions between two compounds to form two new compounds
• General equation: AB + CD → AD + CB
• Key characteristics:
  • Often occur in aqueous solutions
  • Frequently result in formation of a precipitate, gas, or water
• Common types:
  • Precipitation reactions (insoluble solid forms)
  • Neutralization reactions (acid + base → salt + water)
  • Gas-forming reactions
• Examples:
  • Sodium sulfate + Barium chloride → Barium sulfate + Sodium chloride: Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq)
  • Sodium hydroxide + Hydrochloric acid → Sodium chloride + Water: NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
• Double Displacement Reactions (Section 1.2.4) – With examples like sodium sulphate reacting with barium chloride to form barium sulphate precipitate.

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Looking for comprehensive study materials? Explore our Chemical Reactions and Equations: Class 10 Notes for complete coverage of all concepts, formulas, and examples.