Exo and Endothermic reactions

• Exothermic Reaction


  Releases energy (usually as heat) to the surroundings
• Endothermic Reaction


  Absorbs energy (usually as heat) from the surroundings
• Energy Change


  • Exothermic: Energy of products < Energy of reactants
  • Endothermic: Energy of products > Energy of reactants
• Temperature Change


  • Exothermic: Temperature of surroundings increases
  • Endothermic: Temperature of surroundings decreases
• Exothermic Reactions


  • Combustion (e.g., burning wood or fuel)
  • Respiration (glucose + oxygen → carbon dioxide + water + energy)
  • Neutralization (acid + base → salt + water + heat)
• Endothermic Reactions


  • Photosynthesis (carbon dioxide + water + sunlight → glucose + oxygen)
  • Melting ice (solid water absorbs heat to become liquid)
  • Thermal decomposition (e.g., calcium carbonate → calcium oxide + carbon dioxide with heat)
• Exothermic Energy Diagram


  • Reactants have higher energy than products
  • Energy is released to surroundings
• Endothermic Energy Diagram


  • Reactants have lower energy than products
  • Energy is absorbed from surroundings
• Check energy diagrams for reactants and products energy levels
• These notes provide a succinct overview of endothermic and exothermic reactions for Grade 9 Chemistry