Exothermic and Endothermic Reactions

📚 Key Concepts

🔹 Real-Life Example

When you add water to quick lime (used in construction), the mixture becomes very hot – so hot it can burn your skin! This is an exothermic reaction. On the other hand, when you dissolve certain salts like ammonium chloride in water, the solution becomes cold enough to freeze water around it. This is an endothermic reaction, used in instant cold packs for injuries.

Exothermic Reactions: The chemical reactions which proceed with the evolution of heat energy are called exothermic reactions.

Endothermic Reactions: The chemical reactions which proceed with the absorption of heat energy are called endothermic reactions.

🧪 Important Examples

🔸 Exothermic Reactions

  1. All combustion reactions: CH₄ + 2O₂ → CO₂ + 2H₂O + Heat
  2. Respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy
  3. Neutralization: NaOH + HCl → NaCl + H₂O + Heat

🔸 Endothermic Reactions

  1. Photosynthesis: 6CO₂ + 6H₂O + Energy → C₆H₁₂O₆ + 6O₂
  2. Thermal decomposition: CaCO₃ + Heat → CaO + CO₂

🔹 Energy Diagrams

Exothermic: Products have lower energy than reactants

Endothermic: Products have higher energy than reactants

🔍 Advanced: Applications

  • Exothermic: Hand warmers, self-heating food, rocket fuel
  • Endothermic: Instant cold packs, refrigeration, air conditioning
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