NCERT Question 9

What does one mean by exothermic and endothermic reactions? Give examples.

Answer:

• Exothermic Reaction: A chemical reaction that releases heat energy.

  • Example: Combustion of fuel:
    CH₄ + 2O₂→CO₂ + 2H₂O + heat

• Endothermic Reaction: A chemical reaction that absorbs heat energy.

  • Example: Photosynthesis:
    6CO₂ + 6H₂O + sunlight → C₆H₁₂O₆ + 6O₂​