11.3 Applications of Endothermic and Exothermic Reactions in Daily Life

Short Answer Questions

1. What is an exothermic reaction?
   Answer
   An exothermic reaction is a chemical reaction that releases heat energy to the surroundings, increasing the temperature.
2. What is an endothermic reaction?
   Answer
   An endothermic reaction is a chemical reaction that absorbs heat energy from the surroundings, decreasing the temperature.
3. Give an example of an exothermic reaction used in daily life.
   Answer
   Combustion of fuels such as methane (CH₄ + 2O₂ → CO₂ + 2H₂O + heat) releases heat energy for cooking and heating.
4. What chemical is commonly used in self-heating packs?
   Answer
   Calcium oxide (CaO), which reacts with water to release heat.
5. How does respiration demonstrate an exothermic reaction?
   Answer
   Respiration releases energy as glucose reacts with oxygen to form carbon dioxide and water, helping to maintain body temperature.
6. What is the equation for respiration?
   Answer
   C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy
7. What chemical is used in instant cold packs?
   Answer
   Ammonium nitrate (NH₄NO₃), which dissolves in water and absorbs heat.
8. What type of reaction occurs in photosynthesis?
   Answer
   Photosynthesis is an endothermic reaction that absorbs light energy to convert carbon dioxide and water into glucose and oxygen.
9. What is the equation for photosynthesis?
   Answer
   6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂
10. How does baking involve an endothermic reaction?
    Answer
    Heat is absorbed by ingredients, causing chemical changes such as protein denaturation in eggs and the expansion of gases in dough.
11. Why is boiling water considered an endothermic process?
    Answer
    Heat energy is absorbed to break hydrogen bonds in water, allowing the liquid to change into a gas.
12. What is the sign of enthalpy change (ΔH) for exothermic reactions?
    Answer
    Negative (ΔH < 0) because heat is released.
13. What is the sign of enthalpy change (ΔH) for endothermic reactions?
    Answer
    Positive (ΔH > 0) because heat is absorbed.
14. How does the combustion of ethanol demonstrate an exothermic reaction?
    Answer
    The combustion of ethanol (C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O + heat) releases heat energy, which can be used as a fuel.
15. What is the main difference between an exothermic and endothermic reaction?
    Answer
    Exothermic reactions release heat, while endothermic reactions absorb heat.
16. What role does heat play in cooking food?
    Answer
    Heat provides energy for chemical changes in food, such as protein denaturation, caramelization, and evaporation of water.
17. How does enthalpy change relate to heat of reaction?
    Answer
    Enthalpy change (ΔH) measures the heat absorbed or released during a reaction at constant pressure.
18. How can enthalpy change (ΔH) be calculated?
    Answer
    ΔH = mcθ, where m = mass, c = specific heat capacity, and θ = temperature change.
19. Why do self-heating packs get warm when activated?
    Answer
    Self-heating packs contain chemicals that undergo an exothermic reaction, releasing heat to warm the surroundings.
20. Why do instant cold packs feel cold when activated?
    Answer
    Instant cold packs contain chemicals that dissolve in water and absorb heat, creating an endothermic reaction that lowers the temperature.

Explanation Questions

1. Why does respiration release energy while photosynthesis absorbs energy?
   Answer
   Respiration breaks down glucose, releasing stored energy, whereas photosynthesis absorbs light energy to build glucose molecules.
2. Why is combustion an exothermic reaction?
   Answer
   Combustion releases stored chemical energy as heat and light when fuels react with oxygen.
3. Why does the dissolution of ammonium nitrate in water cause a cooling effect?
   Answer
   Ammonium nitrate absorbs heat from the surroundings during dissolution, making the environment cooler.
4. Why do exothermic reactions feel warm to the touch?
   Answer
   Exothermic reactions release heat, which is transferred to the surroundings, increasing temperature.
5. Why does boiling water require continuous heat input?
   Answer
   Boiling water is an endothermic process that requires constant heat to break hydrogen bonds and convert liquid to gas.
6. Why does the combustion of larger hydrocarbons release more energy?
   Answer
   Larger hydrocarbons contain more carbon-hydrogen bonds, which release more energy when broken.
7. Why does photosynthesis require sunlight?
   Answer
   Sunlight provides the necessary energy to drive the conversion of carbon dioxide and water into glucose.
8. Why do self-heating packs generate heat when activated?
   Answer
   Self-heating packs contain chemicals like calcium oxide (CaO) that react with water in an exothermic reaction, releasing heat that warms the surroundings.
9. Why do cold packs feel cold to the touch when activated?
   Answer
   Cold packs use endothermic reactions, such as the dissolution of ammonium nitrate (NH₄NO₃) in water, which absorbs heat from the surroundings, lowering the temperature.
10. Why is heat necessary for cooking food?
    Answer
    Cooking involves endothermic reactions where heat energy is absorbed to break chemical bonds in food, allowing physical and chemical changes such as protein denaturation and caramelization.