NCERT Solutions for Class 7 Science Chapter 5 Changes Around Us: Physical and Chemical

There are various changes that we observe around us every day, like the ripening of fruits, rusting of iron, freezing of water, burning of candles, etc. Out of these, some changes are Physical changes, while others are chemical changes, some are irreversible changes, while others are reversible changes, some changes are fast, while others are slow. In these chapters, students are going to learn about these changes and why some are called physical while others are chemical.

NCERT Solutions for Class 7 Science of Chapter 5 are prepared by subject experts and offer a systematic and structured approach for the exercise problems. These NCERT solutions help students to prepare well for exams by providing detailed solutions to all the exercise questions given in the book.

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NCERT Solutions for Class 7 Science Chapter 5 (Exercise Questions with Answers)

Question 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)

(c) (i) and (iii)

(b) (ii) and (iii)

(d) (iii) and (iv)

Answer:

(c) (i) and (iii)

(i) The state of the substance may or may not change - Physical changes can involve changes in state (like melting or freezing), but no new substance is formed.

(iii) No new substance is formed - In a physical change, the substance remains the same, only its form or state changes.

Question 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?

(i) Stitching cloth to a shirt

Answer (i): Stitching cloth to a shirt - Cannot be reversed: Once stitched, it is hard to undo without damage.

(ii) Twisting of straight string

Answer(ii): Twisting of straight string - Can be reversed: The string can be untwisted.

(iii) Making idlis from a batter

Answer(iii):

Making idlis from a batter - Cannot be reversed: The batter cannot be returned to its original form after steaming.

(iv) Dissolving sugar in water

Answer(iv): Dissolving sugar in water - Can be reversed: Sugar can be recovered by evaporating water.

(v) Drawing water from a well

Answer(v): Drawing water from a well - Can be reversed: Water can be returned to the well.

(vi) Ripening of fruits

Answer(vi): Ripening of fruits - Cannot be reversed: Once ripe, fruits cannot go back to unripe.

(vii) Boiling water in an open pan

Answer(vii): Boiling water in an open pan - Can be reversed: Evaporated water can be obtained back by condensation.

(viii) Rolling up a mat

Answer(viii): Rolling up a mat - Can be reversed: The mat can be unrolled.

(ix) Grinding wheat grains to flour

Answer(ix): Grinding wheat grains to flour - Cannot be reversed: Flour cannot be turned back into grains.

(x) Forming of soil from rocks

Answer(x): Forming of soil from rocks - Cannot be reversed: Soil formation is a slow process and cannot form rock back.

Question 3: State whether the following statements are True or False. In case a statement is False, write the correct statement.

1. Melting of wax is necessary for burning a candle. (True/False)

Answer 1: True

2. Collecting water vapour by condensing involves a chemical change. (True/False)

Answer 2: False

Correct statement: Collecting water vapour by condensing involves a physical change.

3. The process of converting leaves into compost is a chemical change. (True/False)

Answer 3: True

4. Mixing baking soda with lemon juice is a chemical change. (True/False)

Answer 4: True

Question 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—-----------and this is a —----- change.

Answer: rusting, chemical

(ii) Folding a handkerchief is a —----------change and can be —---------.

Answer: physical, reversed

(iii) A chemical process in which a substance reacts with oxygen with evolution of heat is called —-------- and this is a —------- change.

Answer: combustion, chemical

(iv) Magnesium, when burnt in air, produces a substance called —-------. The substance formed is —--------- in nature. Burning of magnesium is a —----------change.

Answer: magnesium oxide, basic, chemical

Question 5: Are the changes of water to ice and water to steam, physical or chemical? Explain.

Answer: Both, the change of water to ice and water to steam are physical changes. In both processes, the chemical composition of water remains the same; only its state changes from liquid to solid or from liquid to gas. No new substance is formed which is a characteristic of physical changes.

Question 6: Is curdling of milk a physical or chemical change? Justify your statement.

Answer: The curdling of milk is a chemical change because, during this process, milk reacts with acid or bacteria, forming new substances like curd. This change cannot be reversed, which makes it a chemical change.

Question 7: Natural factors, such as wind, rain, etc., help in the formation of soil from rocks. Is this change physical or chemical and why?

Answer: The formation of soil from rocks involves both physical and chemical changes. Natural factors like wind, rain and temperature break down rocks into smaller pieces (physical change), while chemical processes, like weathering, also change the minerals in the rocks (chemical change). Both types of changes work together to form soil.

Question 8: Read the following story titled 'Eco-friendly Prithin', and tick the most appropriate option(s) given in the brackets. Provide a suitable title of your choice for the story.

Prithvi is preparing a meal in the kitchen. He chops vegetables, peels potatoes, and cuts fruits (physical changes/chemical changes). He collects the seeds, fruits, and vegetable peels into a clay pot (physical change/ chemical change). The fruits, vegetable peels, and other materials begin to decompose due to the action of bacteria and fungi, forming compost (physical change/chemical change). He decides to plant seeds in the compost and water them regularly. After a few days, he notices that the seeds begin to germinate and small plants start to grow, eventually blooming into colourful flowers (physical change/chemical change). His efforts are appreciated by all his family members.

Answer: Prithvi's Green Kitchen

1. Prithvi chops vegetables, peels potatoes, and cuts fruits are physical changes

2. He collects the seeds, fruits, and vegetable peels into a clay pot are physical change

3. The fruits, vegetable peels, and other materials decompose into compost are chemical change

5. Seeds germinate and grow into plants are chemical change

Question 9: Some changes are given here. Write physical changes in the area marked 'A' and chemical changes in the area marked 'B'. Enter the changes which are both physical and chemical in the area marked 'C

Process of burning a candle; Tearing of paper; Rusting; Curdling of milk; Ripening of fruits; Melting of ice; Folding of clothes; Burning of magnesium and Mixing baking soda with vinegar.

Answer 9: A (Physical changes)

• Tearing of paper

• Melting of iron

• Folding of clothes

B (Chemical Changes)

• Rusting

• Curdling of milk

• Ripening of fruits

• Burning of magnesium

• Mixing baking soda with vinegar

C ( Both physical and chemical changes)

• Process of burning of candle

Question 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?

Answer: In Figure (a), when vinegar reacts with baking soda, carbon dioxide gas is released. This carbon dioxide gas travels through the straw into the test tube with lime water, where it reacts to form calcium carbonate, a white solid substance that makes the lime water appear milky.

Approach to Solve Questions of Class 7 Science Chapter 5

To solve questions from the chapter, students must keep the points given below in mind:

1) Understand the basic concepts like:

• Physical changes

• Chemical changes

• Rusting

• Combustion

• Erosion

2) Read the question carefully

• Try to identify what is given by identifying key terms given in the question, like physical changes, chemical changes, combustion, etc.

• Determine what we need to find out.

3) Try to understand questions by connecting them with real-life examples

• Change in the length of a rubber band by stretching, which is a physical change

• Burning of a candle, which is both a physical as well as chemical change

• Ripening of fruits, which is a chemical change

4) Also, use some common tricks, such as paying attention to key differences like physical and chemical changes.

5). Revise notes timely and practice previous year question papers of the exam, as well as practice mock tests accordingly.

Topics and Subtopics Covered in the NCERT Textbook

1) A substance may change in appearance but remain the same

2) A substance may change in appearance and not remain the same

3) Some other processes involving chemical changes

• Rusting

• Combustion

4) Can physical and chemical changes occur in the same process

5) Are changes permanent

6) Are all changes desirable

7) Some slow natural changes

• Weathering of rocks

• Erosion

Practice Questions for Class 7 Science Chapter 5

Question 1. Which of the following is a chemical change?

1) Melting of wax

2) Tearing of paper

3) Burning of wood

4) Dissolving sugar in water

Answer. Burning produces new substances like ash and gases, making it a chemical change.

Hence, the correct answer is option (3).

Question 2. Which of the following changes is reversible?

1) Rusting of iron

2) Cooking of rice

3) Freezing of water

4) Burning of a candle

Answer: Water can freeze into ice and melt back, making it a reversible physical change.

Hence, the correct answer is option (3).

Question 3. Is a chemical change reversible?

Answer: Typically, chemical changes are not easily reversible. While some chemical reactions can be reversed under specific conditions, it usually requires additional energy or other chemical reactions. Therefore, It is difficult.

NCERT Solutions for Class 7 Science Chapter-wise

The chapter-wise solutions are given below:

NCERT Books and NCERT Syllabus

The NCERT books and syllabus links for class 7 are given below:

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