NCERT Solutions for Class 7 Science Curiosity Chapter 5 help students clearly understand the topic Changes Around Us, which covers the differences between physical and chemical changes. This chapter explains how some changes are reversible (like melting or folding) while others are permanent and form new substances (like rusting or burning).
With simple explanations and real-life examples, the chapter builds strong foundational concepts. These Class 7 Science Chapter 5 solutions are designed to guide students through each question in an easy and logical way, boosting their confidence and helping them score well in exams.
Class 7 Science Curiosity Chapter 5 Changes Around Us: Physical and Chemical
Class 7 Science Curiosity Chapter 5, Changes Around Us, introduces students to the different types of changes we see in our daily lives. It explains how some changes are reversible, like folding paper or melting ice, while others are irreversible, like cooking food or rusting iron.
The chapter also helps students understand the basic difference between physical and chemical changes through simple activities and relatable examples. This chapter builds curiosity by encouraging observation and logical thinking about how and why changes happen around us.
NCERT Class 7 Science Curiosity Chapter 5 Question Answer
Below we have provided the complete NCERT solutions for Class 7 Science Curiosity Chapter 5 Changes Around Us Physical and Chemical. These include all textbook questions, activities, and exercises with clear and accurate answers. The solutions are designed to help students understand key concepts easily and perform better in exams.
Let Us Enhance Our Learning
1. Which of the following statements are the characteristics of a physical change?
(i) The state of the substance may or may not change.
(ii) A substance with different properties is formed.
(iii) No new substance is formed.
(iv) The substance undergoes a chemical reaction.
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iii) (correct)
(d) (iii) and (iv)
Answer: (c) (i) and (iii)
Reason: In physical changes, the state or shape may change, but no new substance is formed.
2. Predict which of the following changes can be reversed and which cannot be reversed. If you are not sure, you may write that down. Why are you not sure about these?
| Change |
Reversed/Not Reversed |
Reason |
| (i) Stitching cloth to a shirt |
Cannot be reversed |
Cloth is cut and stitched permanently |
| (ii) Twisting of straight string |
Can be reversed |
The string can be straightened |
| (iii) Making idlis from batter |
Cannot be reversed |
New substance is formed while cooking |
| (iv) Dissolving sugar in water |
Can be reversed |
Water can be evaporated |
| (v) Drawing water from a well |
Can be reversed |
Water can be put back |
| (vi) Ripening of fruits |
Cannot be reversed |
Permanent biological change |
| (vii) Boiling water in an open pan |
Can be reversed |
Water can be condensed |
| (viii) Rolling up a mat |
Can be reversed |
Mat can be unrolled |
| (ix) Grinding wheat grains to flour |
Cannot be reversed |
Original grains cannot be brought back |
| (x) Forming of soil from rocks |
Cannot be reversed |
Happens over thousands of years |
3. State whether the following statements are True or False. In case a statement is False, write the correct statement.
(i) Melting of wax is necessary for burning a candle.
True
(ii) Collecting water vapour by condensing involves a chemical change.
False
Correct Statement: Collecting water vapour by condensing involves a physical change.
(iii) The process of converting leaves into compost is a chemical change.
True
(iv) Mixing baking soda with lemon juice is a chemical change.
True
4. Fill in the blanks in the following statements:
(i) Nalini observed that the handle of her cycle has got brown deposits. The brown deposits are due to rusting, and this is a chemical change.
(ii) Folding a handkerchief is a physical change and can be reversed.
(iii) A chemical process in which a substance reacts with oxygen with evolution of heat is called combustion, and this is a chemical change.
(iv) Magnesium, when burnt in air, produces a substance called magnesium oxide. The substance formed is basic in nature. Burning of magnesium is a chemical change.
5. Are the changes of water to ice and water to steam, physical or chemical? Explain.
These are physical changes. No new substance is formed. The state of water changes but it remains water in all forms—solid, liquid, or gas.
6. Is curdling of milk a physical or chemical change? Justify your statement.
It is a chemical change because new substances (curd and whey) are formed, and the change is irreversible.
7. Natural factors, such as wind, rain, etc., help in the formation of soil from rocks. Is this change physical or chemical and why?
It is both a physical and chemical change. Physical forces break rocks into smaller particles, and chemical reactions change their composition.
8. Read the following story titled ‘Eco-friendly Prithvi’ and tick the most appropriate option(s).
-
Chopping vegetables, peeling potatoes → Physical changes
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Collecting peels into a pot → Physical change
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Decomposition of waste into compost → Chemical change
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Germination of seeds and flowering → Chemical change
Suggested Title: Prithvi’s Green Kitchen
9. Some changes are given here. Write physical changes in the area marked ‘A’, chemical changes in ‘B’, and both in ‘C’.
| A (Physical) |
C (Both) |
B (Chemical) |
| Tearing of paper |
Burning of candle |
Rusting |
| Melting of ice |
Mixing baking soda with vinegar |
Curdling of milk |
| Folding of clothes |
|
Ripening of fruits |
10. The experiments shown in Fig. 5.11a, b, c, and d were performed. Find out in which case(s) did lime water turn milky and why?
(a) Vinegar and baking soda – Lime water turns milky due to the formation of carbon dioxide. (correct)
(d) Lemon juice and baking soda – Same reason as above.(correct)
(b) Vinegar and salt – No gas is formed.
(c) Lemon juice and vinegar – Both are acids; no gas produced.
Activity-Based Responses
All the activities (5.1 to 5.8) have been explained in the textbook with the intent of hands-on learning. Here's a summary of expected responses:
Activity 5.1: Table of observations – identify if changes are physical or chemical.
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Melting ice cubes – Physical
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Chopping vegetables – Physical
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Boiling water – Physical
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Making popcorn – Chemical
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Cutting paper – Physical
-
Adding beetroot to water – Physical
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Burning wood – ChemicalDrying wet clothes – Physical
-
Making dough balls – Physical
-
Rolling chapatis – Physical
Activity 5.2:
Activity 5.3:
Activity 5.4:
Activity 5.5:
Activity 5.6:
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Paper catches fire when focused sunlight increases temperature
-
Ignition temperature needed for combustion
-
Combustion needs fuel, oxygen, and heat
Activity 5.7:
Activity 5.8:
-
Melting ice, boiling water → Reversible
-
Making popcorn, chopping vegetables → Irreversible
-
Some changes can be reversed, some cannot.
NCERT Solutions for Class 7 Science Chapter 5 Extra Questions
Below we have shared 15 extra questions and answers from Class 7 Science Chapter 5 Changes Around Us. These questions are explained in simple words to help you understand the chapter better. They cover important topics like physical and chemical changes with easy examples. These will help you revise and do well in your exams.
1. What is a physical change?
A physical change is a change in which a substance undergoes a change in its physical properties such as shape, size, appearance, or state without forming a new substance. Examples include melting of ice, tearing paper, and dissolving sugar in water.
2. What is a chemical change?
A chemical change is a change in which one or more new substances are formed with different properties. This change is usually irreversible. Examples include burning of paper, rusting of iron, and curdling of milk.
3. What happens when vinegar is mixed with baking soda?
When vinegar is mixed with baking soda, a chemical reaction occurs, releasing carbon dioxide gas. This gas forms bubbles. When passed through lime water, the lime water turns milky, confirming the presence of carbon dioxide — a clear sign of chemical change.
4. Why is rusting of iron considered a chemical change?
Rusting is considered a chemical change because iron reacts with moisture and oxygen from the air to form iron oxide (rust), which is a new substance with different properties. The change is irreversible.
5. What are the conditions required for combustion?
Three things are essential for combustion:
(i) A combustible substance (fuel),
(ii) Oxygen (air),
(iii) Heat (to reach ignition temperature).
All three must be present for a substance to catch and sustain fire.
6. Give two examples of reversible changes.
-
Melting of ice: Water can be frozen back into ice.
-
Dissolving sugar in water: The sugar can be recovered by evaporating the water.
7. What is ignition temperature?
It is the minimum temperature at which a substance catches fire. If a fuel does not reach this temperature, it will not ignite even if oxygen is present.
8. Is boiling of water a physical or chemical change? Why?
Boiling of water is a physical change. It only changes the state of water from liquid to gas (steam) without forming a new substance. The process is also reversible.
9. What kind of change is curdling of milk?
Curdling of milk is a chemical change. New substances like curd and whey are formed due to the action of bacteria or acids. This change cannot be reversed.
10. Which type of change is the burning of a candle?
Burning of a candle involves both physical and chemical changes. Melting of wax is a physical change, but the burning of wax vapours to produce carbon dioxide and water is a chemical change.
11. What happens to lime water when carbon dioxide is passed through it?
Lime water turns milky. This happens because carbon dioxide reacts with calcium hydroxide in the lime water to form calcium carbonate, a white insoluble substance.
12. What is weathering of rocks?
Weathering is the breaking down of rocks into smaller pieces due to temperature changes, rain, wind, and plant roots. It involves both physical and chemical changes and eventually leads to the formation of soil.
13. Why does a candle go out when covered with a glass tumbler?
The candle goes out because the oxygen inside the tumbler gets used up. Since oxygen is essential for combustion, its absence stops the burning process.
14. What is erosion?
Erosion is the wearing away and movement of soil and rock particles by natural agents like wind and water. It is a physical change because the material itself is not chemically altered.
15. Why is ripening of fruits considered a chemical change?
Ripening of fruits is a chemical change because enzymes inside the fruit convert starch into sugar and alter its colour, taste, and smell. These changes are permanent and result in new substances being formed.
NCERT Class 7 Science Curiosity Chapter 5 Question Answer PDF
Below we have provided the detailed question and answer PDF for NCERT Class 7 Science Curiosity Chapter 5 Changes Around Us: Physical and Chemical. This PDF includes answers to all textbook questions, exercises, and activities in easy and student-friendly language.
It is designed to help students clearly understand the difference between physical and chemical changes through examples and explanations. This resource is perfect for revision and scoring better marks in exams.
