Physical and Chemical Changes — Class 7 Science NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 7 Science chapter "Physical and Chemical Changes" — 8 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 7 Science chapter "Physical and Chemical Changes" — 8 important questions with detailed answers for CBSE b…
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Key Questions Covered:
- Define physical change.
- Define chemical change.
- Distinguish between physical and chemical changes with two examples each.
- What are the signs of a chemical change?
- Is freezing of water a physical or chemical change? Why?
- Is burning of magnesium a physical or chemical change? Explain.
- + 2 more questions in the full chapter
Solutions Summary:
| Question | Status |
|---|---|
| Define physical change. | ✓ Solved |
| Define chemical change. | ✓ Solved |
| Distinguish between physical and chemical changes with tw… | ✓ Solved |
| What are the signs of a chemical change? | ✓ Solved |
| Is freezing of water a physical or chemical change? Why? | ✓ Solved |
| Is burning of magnesium a physical or chemical change? Ex… | ✓ Solved |
Showing 6 of 8 questions
Q1: Define physical change.
A physical change is a change in which only the physical properties of a substance change.
The substance remains the same chemically.
No new substance is formed.
Example: Melting of ice, boiling of water, breaking of glass.
Q2: Define chemical change.
A chemical change is a change in which a new substance with different chemical properties is formed.
The original substance is transformed into one or more new substances.
Example: Burning of wood, rusting of iron, digestion of food.
Q3: Distinguish between physical and chemical changes with two examples each.
Physical change: No new substance formed; reversible or irreversible change in physical properties only.
Examples: Melting of butter, tearing of paper
Chemical change: New substance formed; generally not easily reversible; change in chemical properties.
Examples: Burning of candle, cooking of food
Q4: What are the signs of a chemical change?
Signs of chemical change:
- Change in colour
- Evolution of gas
- Change in temperature (heat absorbed or released)
- Formation of a precipitate
- Change in smell
Q5: Is freezing of water a physical or chemical change? Why?
Freezing of water is a physical change.
Water changes from liquid state to solid state (ice).
No new substance is formed and water molecules remain the same chemically.
It is reversible - ice can be melted back to water.
Q6: Is burning of magnesium a physical or chemical change? Explain.
Burning of magnesium is a chemical change.
Magnesium reacts with oxygen to form magnesium oxide (white powder).
2Mg + O₂ → 2MgO
A new substance (magnesium oxide) is formed with different properties.
The change is not easily reversible.
Showing 6 of 8 questions. Visit the full page for complete solutions.
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