Class 10 Chemistry – Chapter 1 Chemical Reactions & Equations
1. Why should magnesium ribbon be cleaned before burning?
• Magnesium ribbon has a layer of magnesium oxide on its surface.
• This layer prevents magnesium from burning easily.
2. Why are respiration and photosynthesis considered chemical reactions?
• Both involve chemical changes.
• New substances are formed with release or absorption of energy.
3. Why is burning of coal a chemical reaction?
• Coal reacts with oxygen.
• New substances like CO₂ and ash are formed.
4. What is corrosion?
• Corrosion is the slow destruction of metals by air, moisture or chemicals.
5. What is rancidity?
• Oxidation of fats and oils causing bad smell and taste.
6. Why is rusting faster in coastal areas?
• High moisture and salt content.
• Faster oxidation of iron.
7. Why are food items flushed with nitrogen?
• Prevents oxidation.
• Prevents rancidity.
8. Why is respiration an exothermic reaction?
• Energy is released.
• Glucose breaks into CO₂ and water.
9. What is oxidation?
• Addition of oxygen OR removal of hydrogen.
10. What is reduction?
• Removal of oxygen OR addition of hydrogen.
11. Why oxidation and reduction occur together?
• One loses electrons.
• Other gains electrons.
12. Why is decomposition opposite of combination reaction?
• Combination forms one product.
• Decomposition breaks one compound.
,13. Why is electrolysis a decomposition reaction?
• Electricity breaks compounds.
14. Why is silver chloride kept in dark bottles?
• It decomposes in sunlight.
15. Why does copper sulphate change colour with iron nail?
• Iron displaces copper.
• Green iron sulphate forms.
16. Why is cooking a chemical change?
• New substances form.
• Irreversible.
17. Why is respiration slow combustion?
• Energy released slowly.
• No flame.
18. Why must equations be balanced?
• Law of conservation of mass.
19. Why are decomposition reactions endothermic?
• Energy is absorbed.
20. Why are displacement reactions redox reactions?
• Oxidation and reduction both occur.
21. Why is dissolution of CO₂ in water a chemical change?
• Carbonic acid forms.
22. Why is respiration not combustion?
• No flame.
• Low temperature.
23. Why is precipitation a double displacement reaction?
• Exchange of ions.
24. Why does iron not rust in boiled water with oil?
• No oxygen contact.
25. Why is LPG odourless and mercaptan added?
• Leak detection.
26. Why is photosynthesis endothermic?
• Absorbs sunlight energy.
27. Why are antioxidants added to food?
• Prevent oxidation.
, 28. Why does aluminium not corrode easily?
• Protective oxide layer.
29. Why does lime water turn milky with CO₂?
• Calcium carbonate forms.
30. Why is respiration necessary?
• Releases energy.
Q31. Why is rusting of iron faster in acidic medium?
Answer:
• Acids increase the rate of oxidation.
• They speed up the corrosion process.
Q32. Why is decomposition of calcium carbonate a thermal decomposition?
Answer:
• Heat is required to break calcium carbonate.
• Calcium oxide and carbon dioxide are formed.
Q33. Why does copper not displace iron from iron sulphate solution?
Answer:
• Copper is less reactive than iron.
• Less reactive metals cannot displace more reactive ones.
Q34. Why is burning of magnesium a combination reaction?
Answer:
• Magnesium combines with oxygen.
• A single product (magnesium oxide) is formed.
Q35. Why is curd formation from milk a chemical change?
Answer:
• New substances are formed.
• The change is irreversible.
1. Why should magnesium ribbon be cleaned before burning?
• Magnesium ribbon has a layer of magnesium oxide on its surface.
• This layer prevents magnesium from burning easily.
2. Why are respiration and photosynthesis considered chemical reactions?
• Both involve chemical changes.
• New substances are formed with release or absorption of energy.
3. Why is burning of coal a chemical reaction?
• Coal reacts with oxygen.
• New substances like CO₂ and ash are formed.
4. What is corrosion?
• Corrosion is the slow destruction of metals by air, moisture or chemicals.
5. What is rancidity?
• Oxidation of fats and oils causing bad smell and taste.
6. Why is rusting faster in coastal areas?
• High moisture and salt content.
• Faster oxidation of iron.
7. Why are food items flushed with nitrogen?
• Prevents oxidation.
• Prevents rancidity.
8. Why is respiration an exothermic reaction?
• Energy is released.
• Glucose breaks into CO₂ and water.
9. What is oxidation?
• Addition of oxygen OR removal of hydrogen.
10. What is reduction?
• Removal of oxygen OR addition of hydrogen.
11. Why oxidation and reduction occur together?
• One loses electrons.
• Other gains electrons.
12. Why is decomposition opposite of combination reaction?
• Combination forms one product.
• Decomposition breaks one compound.
,13. Why is electrolysis a decomposition reaction?
• Electricity breaks compounds.
14. Why is silver chloride kept in dark bottles?
• It decomposes in sunlight.
15. Why does copper sulphate change colour with iron nail?
• Iron displaces copper.
• Green iron sulphate forms.
16. Why is cooking a chemical change?
• New substances form.
• Irreversible.
17. Why is respiration slow combustion?
• Energy released slowly.
• No flame.
18. Why must equations be balanced?
• Law of conservation of mass.
19. Why are decomposition reactions endothermic?
• Energy is absorbed.
20. Why are displacement reactions redox reactions?
• Oxidation and reduction both occur.
21. Why is dissolution of CO₂ in water a chemical change?
• Carbonic acid forms.
22. Why is respiration not combustion?
• No flame.
• Low temperature.
23. Why is precipitation a double displacement reaction?
• Exchange of ions.
24. Why does iron not rust in boiled water with oil?
• No oxygen contact.
25. Why is LPG odourless and mercaptan added?
• Leak detection.
26. Why is photosynthesis endothermic?
• Absorbs sunlight energy.
27. Why are antioxidants added to food?
• Prevent oxidation.
, 28. Why does aluminium not corrode easily?
• Protective oxide layer.
29. Why does lime water turn milky with CO₂?
• Calcium carbonate forms.
30. Why is respiration necessary?
• Releases energy.
Q31. Why is rusting of iron faster in acidic medium?
Answer:
• Acids increase the rate of oxidation.
• They speed up the corrosion process.
Q32. Why is decomposition of calcium carbonate a thermal decomposition?
Answer:
• Heat is required to break calcium carbonate.
• Calcium oxide and carbon dioxide are formed.
Q33. Why does copper not displace iron from iron sulphate solution?
Answer:
• Copper is less reactive than iron.
• Less reactive metals cannot displace more reactive ones.
Q34. Why is burning of magnesium a combination reaction?
Answer:
• Magnesium combines with oxygen.
• A single product (magnesium oxide) is formed.
Q35. Why is curd formation from milk a chemical change?
Answer:
• New substances are formed.
• The change is irreversible.
