What is the difference between exothermic and endothermic reactions?

Exothermic Reactions

• Definition: Reactions that release heat energy to the surroundings.
• System behavior: System loses energy, surroundings get warmer.
• Enthalpy change (ΔH): Negative (energy goes out).
• Examples:
  • Combustion of fuels (burning wood, petrol).
  • Neutralization (acid + base → salt + water).
  • Respiration (glucose breakdown releases energy).

Endothermic Reactions

• Definition: Reactions that absorb heat energy from the surroundings.
• System behavior: System gains energy, surroundings get cooler.
• Enthalpy change (ΔH): Positive (energy goes in).
• Examples:
  • Photosynthesis (plants absorb sunlight).
  • Thermal decomposition (CaCO₃ → CaO + CO₂).
  • Dissolving salts like ammonium nitrate in water.

Key Difference in One Line

• Exothermic: Heat exits (released), surroundings warm up.
• Endothermic: Heat enters (absorbed), surroundings cool down.