Types of Chemical Reactions

Key Notes :

Combination (Synthesis) Reaction:

• Description: Two or more reactants combine to form a single product.
  A + B → AB

• Example:
  2H₂ + O₂ → 2H₂O
• Key Characteristics: Energy is often released as heat or light.

Decomposition Reaction:

• Description: A single compound breaks down into two or more simpler substances.
  AB → A + B

• Example:
  2HgO → 2Hg + O₂​
• Types:
  • Thermal decomposition (heat-induced)
  • Electrolytic decomposition (electricity-induced)
  • Photochemical decomposition (light-induced)

Displacement Reaction:

• Description: One element displaces another in a compound.
  A + BC → AC + B

• Example:
  Zn + CuSO₄ → ZnSO₄ + Cu
• Key Characteristics: Often involves metals or halogens.

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Double Displacement Reaction:

Description: Exchange of ions between two compounds.
AB + CD → AD + CB

Example:
NaCl + AgNO₃ → NaNO₃ + AgCl

Types:

• Precipitation Reaction: Formation of an insoluble product (precipitate).
• Neutralization Reaction: Acid reacts with base to form salt and water.

Redox Reaction:

Description: Transfer of electrons where one substance is oxidized, and another is reduced.

• Oxidation: Loss of electrons.
• Reduction: Gain of electrons.

Example:
Zn + CuSO₄ → ZnSO₄ + Cu

Key Characteristic: Involves changes in oxidation states.

Combustion Reaction:

• Description: A substance reacts with oxygen, releasing heat and light.
  Fuel + O₂ → CO₂ + H₂O

• Example:
  CH₄ + 2O₂ → CO₂ + 2H₂O
• Key Characteristics: Exothermic process.

Endothermic and Exothermic Reactions:

• Endothermic Reaction: Absorbs energy from the surroundings.
  Example: Photosynthesis.

• Exothermic Reaction: Releases energy to the surroundings.
  Example: Combustion.

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