What does one mean by exothermic and endothermic reactions? Give examples.
Exothermic reactions are reactions in which heat is released along with the formation of products. This makes the reaction mixture warm. Examples include burning of natural gas (CH₄ + 2O₂ → CO₂ + 2H₂O), respiration (C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy), decomposition of vegetable matter into compost, and formation of water from hydrogen and oxygen (2H₂ + O₂ → 2H₂O).
Endothermic reactions are reactions that absorb heat during the process. An activity involves adding substances like ammonium nitrate, potassium sulphate, anhydrous copper sulphate, and iron fillings to water, and measuring temperature changes to identify which reactions are endothermic.
Explanation
The textbook clearly defines exothermic reactions as those where heat is released along with product formation, making the mixture warm. Multiple examples are provided including burning of natural gas, respiration, decomposition of vegetable matter into compost, and formation of water. For endothermic reactions, the context mentions them in a group activity where students measure temperature changes when various substances are added to water, but does not explicitly define or provide specific examples of endothermic reactions.