Imp Questions For All Chapters – General Science Class 7
Changes – Physical and Chemical
Short Questions
1. What is a change?
→ A change is an alteration in the shape, size, color, or state of a substance.
2. What are the two main types of changes?
→ Physical changes and Chemical changes.
3. What is a physical change?
→ A physical change is when only the appearance changes but the substance remains the same, like melting ice.
4. What is a chemical change?
→ A chemical change creates a new substance with different properties, like rusting of iron.
5. Give an example of a physical change.
→ Melting of ice is a physical change because it turns into water but remains H₂O.
6. Give an example of a chemical change.
→ Burning of paper is a chemical change as it forms ash and cannot be reversed.
7. What is a reversible change?
→ A reversible change is a change that can be undone, like freezing water into ice.
8. What is an irreversible change?
→ An irreversible change is a change that cannot be undone, like cooking food.
9. What is a periodic change?
→ A periodic change occurs at regular intervals, like the change of seasons.
10. What is a non-periodic change?
→ A non-periodic change occurs at irregular intervals, like an earthquake.
11. What is corrosion?
→ Corrosion is the slow destruction of metals due to air, water, or chemicals, like rusting of iron.
12. What is galvanization?
→ Galvanization is the process of coating iron with zinc to prevent rusting.
13. Why is tinning done on copper and brass utensils?
→ Tinning protects copper and brass from corrosion and makes them safe for cooking.
14. Why does a wet handkerchief dry slowly but gets wet quickly?
→ Water soaks in quickly but takes time to evaporate, depending on heat and air.
15. What happens when sugar is heated?
→ It melts first (physical change) and then turns black (chemical change).
Long Questions
1. What is the difference between physical and chemical changes?
→ In a physical change, only the appearance or state changes, and no new substance is formed (e.g., melting ice). In a chemical change, a new substance is created with different properties (e.g., rusting of iron).
2. What are natural and man-made changes? Give examples.
→ Natural changes happen on their own, like ripening of fruits and rainfall. Man-made changes are caused by humans, like building a house or baking bread.
3. What is corrosion? How can it be prevented?
→ Corrosion is the slow damage of metals due to moisture and air, like rusting of iron. It can be prevented by painting, galvanizing, or oiling metal surfaces.
4. What are fast and slow changes? Give examples.
→ Fast changes occur quickly, like bursting a balloon. Slow changes take time, like growth of a plant.
5. Why should we check the expiry date while buying canned food?
→ Expired food may contain harmful bacteria and toxins that cause food poisoning. Checking the expiry date ensures safety and freshness.
6. Why are wooden articles polished?
→ Polishing prevents wood from absorbing moisture, protects it from damage, and gives it a shiny, smooth appearance.
7. Why does a wet handkerchief take longer to dry than a dry one getting wet?
→ Water soaks into a dry handkerchief instantly, while drying takes time as water must evaporate into the air.
8. Why do copper and brass utensils need tin coating?
→ Tin coating prevents reaction with food and stops corrosion, keeping the utensils safe and long-lasting.
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