RBSE Class 7 Science Chapter 5 Question Answer Changes Around Us Physical and Chemical
By tackling theseRBSE Solutions Class 7 Scienceand RBSE Class 7 Science Chapter 5 Changes Around Us Physical and Chemical Question Answer, students will build a solid foundation in the topic.
Changes Around Us Physical and Chemical Class 7 Question Answer
RBSE Class 7 Science Chapter 5 Changes Around Us Physical and Chemical Question Answer
Class 7 Science Curiosity Chapter 5 Question Answer (Exercise)
(Let Us Enhance Our Learning)
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)
(b) (ii) and (iii)
(c) (i) and (iii)
(d) (iii) and (iv)
Answer:
(c) (i) and (iii)
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
(ii) Twisting of straight string
(iii) Making idlis from a batter
(iv) Dissolving sugar in water
(v) Drawing water from a well
(vi) Ripening of fruits
(vii) Boiling water in an open pan
(viii) Rolling up a mat
(ix) Grinding wheat grains to flour
(x) Forming of soil from rocks
Answer:
(i) Stitching cloth to a shirt: Irreversible Because after making shirt of pieces of cloth, it can’t be change into cloth.
(ii) Twisting of straight string : Reversible
(iii) Making idlis from a batter : Irreversible Because idlis cannot be converted again into batter.
(iv) Dissolving sugar in water : Reversible
(v) Drawing water from a well : Reversible
(vi) Ripening of fruits : Irreversible Because ripening of fruits is a chemical change and starch inside it converted into sugar and structure is changed. Ripen fruits cannot be converted into unriped fruits.
(vii) Boiling water in an open pan: Irreversible Because boiling water in an open pan, water will evaporate and cannot get back as water. Even boiling water in a covered pan, water can be get back with the process of condensation.
(viii) Rolling up a mat : Reversible
(ix) Grinding wheat grains to flour : Irreversible Shape and size of wheat grain changes completely. Grains cannot be formed after grinding flour. It is a physical change but irreversible.
(x) Forming of soil form rocks : Irreversible It is a long time procedure and chemical and physical both changes are included. The soil formed cannot be converted back into rocks.
Question 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/False)
(ii) Collecting water vapour by condensing involves a chemical change. (True/False)
(iii) The process of converting leaves into compost is a chemical change. (True/False)
(iv) Mixing baking soda with lemon juice is a chemical change. (True/False)
Answer:
(i) True
(ii) False; Correct statement: Collecting water vapour by condensing involves a physical change not a chemical change.
(iii) True
(iv) 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:
rust, chemical
(ii) Folding a handkerchief is a ______ change and can be ______
Answer:
physical, reversible
(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:
Changing of water to ice and water to steam is a physical change because only state of matter changes. No new substance formed.
Question 6.
Is curdling of milk a physical or chemical change? Justify your statement.
Answer:
Curdling of milk is a chemical change because a new substance curd is formed by chemical reactions.
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:
Air, rain, temperature etc. natural factors forms soil by breaking rocks. Both physical and chemical changes can be seen in soil formation together. When rocks broken into small pieces is a physical change when air, water and gases change minerals in rocks, it is chemical change. So, soil formation is a joint (physical + chemical) reaction.
Question 8.
Read the following story titled ‘Ecofriendly Prithvi’ 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 material 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 seed begin to germinate and small plant start to grow, eventually blooming into colourful flowers (physical change/chemical change). His efforts are appreciated by all his family members.
Answer:
Title – Changes in Prithvi’s Story Chopping vegetable, peel potatoes, and cuts fruits – Physical change Collecting peels in clay pot – Physical change Forming compost – Chemical change Blooming of flowers – 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:
Classification of changes :
‘A’ → Physical changes – Tearing of paper, Melting of ice, 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 Burning of candle.
Question 10.
The experiments shown in Fig. 5.11 a, b, c, and d were performed. Find out in which case(s) did lime water turn milky and why?
because a new substance curd is formed by chemical reactions.
Answer:
Lime water turns milky in case (a) and (d) because in both of these CO2gas is emitted by the reaction of acid and baking soda which turns lime water milky.
(a) Vinegar + Baking soda → CO2+ Other substances
(b) Lemon juice + Baking soda → CO2+ Other substances
There will be no change in lime water in case (b) and (c), because CO2gas is not emitted there.
Changes Around Us Physical and Chemical Class 7 Questions and Answers (Intext)
(Page – 58)
Question 1.
Can we arrange these changes into categories?
Answer:
It is discussion about the changes happening around us in question which can be categorised as follows Physical changes, chemical changes, desirable and undesirable changes, reversible and irreversible changes.
(Page No. 59)
Question 2.
Do you get the same paper back when you unfold the objects of paper?
Answer:
No. the paper does not remain same but with some crease due to folding. Because it is a physical change.
Question 3.
Crush a small piece of chalk into powder. Can you get the chalk piece back from powder?
Answer:
No, we cannot get the chalk piece back from powder. It is an irreversible change.
(Page No. 61)
Question 4.
What do you infer about the gas formed by mixing vinegar and baking soda?
Answer:
Mixing vinegar and baking soda results in the formation of carbon dioxide gas.
Vinegar + Baking Soda → Carbon dioxide + Other substances
Question 5.
Let us find out whether the presence of oxygen is essential for combustion.
Answer:
Yes, combustion is a chemical process in which any substance reacts with oxygen and produces heat and/or light is called combustion.
(Page No. 64)
Question 6.
What changes take place when a candle is lit? Let us explore.
Answer:
Melting and solidification of wax → Physical change
The burning of wax vapour → Chemical change
(Page No 66)
Question 7.
Once something has undergone a change, can we get it back in its original form?
Answer:
Some things can get back in the original form but some cannot. Ex.: Melting of ice, changing of water into water vapour are reversible because can be make ice and water by condensation. But the chopped vegetable, and popcorn cannot be get back in its original form.