Chemical Reactions and Equations

Breaking and forming of chemical bonds, where reactants are transformed into products, are called chemical reactions. These chemical reactions depend on factors such as temperature, air moisture, reactants, etc.

• Combination Reaction
  
  • A reaction in which a single product is formed from two or more reactants is known as a combination reaction.
  • A combination reaction is also known as a synthesis reaction because simpler substances join together to form complex compounds.
  • Example: Making of Lime water
    CaO(s) + H₂O(l) → Ca(OH)₂ (aq) + Heat
    (Quick lime) (Slaked lime)
• Exothermic Reaction
  
  • A reaction in which heat is released when the products are formed is called an exothermic chemical reaction.
  • Exothermic Reaction is a type of Combination Reaction.
  • Example: Burning of natural gas
    CH₄(g) + 2O₂(g) + Heat → CO₂(g) + 2H₂O(g)
• Endothermic Reaction
  
  • A reaction in which energy is absorbed by the surroundings is called an endothermic chemical reaction.
  • Endothermic reaction is a type of combination reaction.
  • Example: Melting of ice
    H₂O(s) + Heat → H₂O(l)
• Decomposition Reaction
  
  • A reaction in which a single reactant breaks down to give simpler products is called a decomposition reaction.
  • Decomposition reactions can happen with the help of electricity, light, or heat.
  • Example: Burning of Sulphur
    2FeSO₄(s) + Heat → Fe₂O₃(s) + SO₂(g) + SO₃(g)
    (Ferrous sulfate) (Ferric oxide)
• Single Displacement Reaction
  
  • A reaction in which a single element displaces another element from a compound is called a displacement reaction.
  • In a single displacement reaction, the more reactive metal displaces the less reactive metal.
  • Example: Zinc displacing Hydrogen from hydrochloric acid
    Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)
• Double Displacement Reaction
  
  • A reaction in which two compounds exchange their elements to form two new compounds.
  • Any reaction that produces an insoluble substance is called a precipitate. This reaction is called precipitation.
  • Example: Barium sulfate precipitating
    Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq)
    (Sodium sulfate) (Barium chloride) (Barium sulfate) (Sodium chloride)
• Oxidization and Reduction
  
  • A process in which the element gains hydrogen is called oxidization.
  • A reaction in which the element loses oxygen is called reduction.
  • Example: Hydrogen reducing copper oxide to copper and water
    CuO + H₂ + Heat → Cu + H₂O

• Corrosion
  When the substances present around it, such as moisture, acids, etc., attack a metal, it is said to corrode, and this process is called corrosion. Corrosion causes damage to car bodies, bridges, iron railings, ships, and all objects made of metals, especially those of iron. Examples: Rust on Iron, Tarnish on Silver, Blue-green patina on copper, etc.
• Rancidity
  When fats and oils are oxidized, their taste and smell change; this process is called rancidity. Antioxidant substances are added to foods containing oil and fat to prevent rancidity. Keeping food in air-tight containers also slows down the process of oxidation. Examples: Milk in heat, Butter left in the open, Potato chips exposed to air, etc.