14/09/2026
Exothermic and Endothermic Reactions
Chemical reactions involve changes in energy. Based on how heat energy is transferred, reactions are classified as exothermic or endothermic.
Exothermic Reaction
An exothermic reaction is a reaction in which heat is released to the surroundings. As a result, the surroundings become warmer. The products have less energy than the reactants, and the change in enthalpy (ΔH) is negative.
Example:
CH₄ + 2O₂ → CO₂ + 2H₂O + heat
Examples: Combustion, burning of fuels, and many neutralization reactions.
Endothermic Reaction
An endothermic reaction is a reaction in which heat is absorbed from the surroundings. The surroundings may become cooler. The products have more energy than the reactants, and the change in enthalpy (ΔH) is positive.
Example:
CaCO₃ + heat → CaO + CO₂
Examples: Photosynthesis and thermal decomposition of calcium carbonate.
Conclusion
The main difference is simple: exothermic reactions release heat, while endothermic reactions absorb heat.
