General Science Important Questions Chapter 14 Measurement and Effects of Heat Class 8 Maharashtra Board

Imp Questions For All Chapters – General Science Class 8

Short Questions

1. What is a chemical change?

• A chemical change is a process where a new substance is formed with different properties.

2. Give one example of a chemical change.

• Rusting of iron is a chemical change.

3. What is a physical change?

• A physical change is a change where no new substance is formed and the change is reversible.

4. Give one example of a physical change.

• Melting of ice is a physical change.

5. What happens when iron rusts?

• Iron reacts with oxygen and water to form iron oxide (rust).

6. What type of bond is present in sodium chloride (NaCl)?

• Ionic bond is present in sodium chloride.

7. What type of bond is present in water (H₂O)?

• Covalent bond is present in water.

8. What is an ionic bond?

• An ionic bond is formed when one atom transfers electrons to another atom.

9. What is a covalent bond?

• A covalent bond is formed when two atoms share electrons.

10. Which gas is necessary for combustion (burning)?

• Oxygen (O₂) is necessary for combustion.

11. What gas is released when baking soda reacts with lemon juice?

• Carbon dioxide (CO₂) gas is released.

12. Why is photosynthesis a chemical change?

• Because new substances like glucose and oxygen are formed.

13. What happens when iron nails are placed in copper sulphate solution?

• The iron nails get coated with copper, and the solution changes color.

14. What is a reactant?

• A reactant is a substance that takes part in a chemical reaction.

15. What is a product?

• A product is a new substance formed after a chemical reaction.

Long Questions

1. What are the differences between physical and chemical changes?

• A physical change does not form a new substance and can be reversed (e.g., melting ice). A chemical change forms a new substance with different properties and is irreversible (e.g., burning wood).

2. Why is rusting of iron considered a chemical change?

• Rusting happens when iron reacts with oxygen and water, forming iron oxide (rust). Since a new substance is created with different properties, it is a chemical change.

3. What happens when baking soda is added to lemon juice?

• Baking soda reacts with the citric acid in lemon juice, producing carbon dioxide gas and bubbles. This is a chemical change because a gas is released and the reaction cannot be reversed.

4. Why is respiration a chemical change?

• In respiration, glucose reacts with oxygen to form carbon dioxide, water, and energy. Since new substances are formed, and energy is released, respiration is a chemical change.

5. What are ionic and covalent bonds?

• An ionic bond is formed when one atom transfers electrons to another (e.g., NaCl). A covalent bond is formed when atoms share electrons to form a molecule (e.g., H₂O).

6. What happens when iron nails are placed in copper sulphate solution?

• Iron reacts with copper sulphate solution, forming iron sulphate and depositing copper on the nails. The color of the solution changes, proving a chemical reaction has taken place.

7. Why does food spoil over time?

• Food spoils due to chemical reactions caused by bacteria, oxygen, and heat. These changes alter the smell, color, and taste of food, making it unsafe to eat.

8. Why is photosynthesis a chemical change?

• Photosynthesis happens when plants use carbon dioxide, water, and sunlight to produce glucose and oxygen. Since new substances are formed, and energy is stored, it is a chemical change.