NCERT Solutions for Class 7 Science Chapter 6 Physical and Chemical Changes

These NCERT Solutions for Class 7 Science Chapter 6 Physical and Chemical Changes Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Physical and Chemical Changes NCERT Solutions for Class 7 Science Chapter 6

Class 7 Science Chapter 6 Physical and Chemical Changes Textbook Exercise Questions and Answers

Question 1.
Classify the changes involved in the following processes as physical or chemical changes:
a. Photosynthesis
b. Dissolving sugar in water
c. Burning of coal
d. Melting of wax
e. Beating aluminium to make aluminium foil
f. Digestion of food
Answer:
a. Chemical change
b. Physical change
c. Chemical change
d. Physical change
e. Physical change
f. Chemical change

Question 2.
State whether the following statements are true or false. In case a statement is false, write the corrected statement in your notebook.
a. Cutting a log of wood into pieces is a chemical change.
b. Formation of manure from leaves is a physical change.
c. Iron pipes coated with zinc do not get rusted easily.
d. Iron and rust are the same substance.
e. Condensation of steam is not a chemical change.
Answer:
a. False, it is physical change.
b. False, it is chemical change.
c. True.
d. False, they are different substances.
e. True

Question 3.
Fill in the blanks in the following statements:
a. When carbon dioxide is passed through lime water, it turns milky due to the formation of …………………
b. The chemical name of baking soda is …………………
c. Two methods by which rusting of iron can be prevented are ………………… and …………………
d. Changes in which only ………………… properties of a substance change are called physical changes.
e. Changes in which new substances are formed are called ………………… changes.
Answer:
a. calcium carbonate
b. sodium hydrogen carbonate
c. painting or greasing, galvanisation
d. physical
e. chemical

Question 4.
When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain.
Answer:
When baking soda (Sodium hydrogen-carbonate) is mixed with lemon juice (citric acid), bubbles are formed. These bubbles are formed due to the evolution of carbon dioxide gas. This is a chemical change. In this change, citric acid contained in lemon juice reacts with sodium hydrogen carbonate which results in the evolution of carbon dioxide gas. The reaction can be represented as follows:
Lemon juice + Baking soda → Carbon dioxide + Other substances

Question 5.
When a candle burns, both physical and chemical changes take place. Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place.
Answer:
When a candle bums, both physical and chemical changes occur:

Physical changes: On heating, melting candle is a physical change since it again turns into solid wax on cooling.
Chemical changes: The wax vapours bum to give new substances like carbon dioxide, carbon soot, water vapour, heat and light. This is a chemical change.

LPG is another example in which the physical change occurs when LPG comes out of the cylinder and is converted from liquid to gaseous state and the chemical change occurs when gas burns in air.

Question 6.
How would you show that setting of curd is a chemical change?
Answer:
The curd is formed from milk. Both the curd and the milk have different properties. Also, once the curd is formed, it cannot be reversed back into milk. So, there is a formation of new substance with different properties and also it is an irreversible process. Hence, setting of curd is a chemical change.

Question 7.
Explain why burning of wood and cutting it into small pieces are considered as two different types of changes.
Answer:
Burning of wood is a chemical change because in burning, new substances are formed and heat and light are produced. Wood + Oxygen → Carbon dioxide + Charcoal + Heat + Light
But cutting it into small pieces is a physical change because no new substance is formed in this. We can only reduce the size of wood by cutting which is a physical property.

Question 8.
Describe how crystals of copper sulphate are prepared.
Answer:
Crystals of copper sulphate are prepared by the method of crystallisation. A cup of water is taken in a beaker. Few drops of dilute sulphuric acid are added to this. The water is then heated and when it starts boiling, copper sulphate powder is added. Copper sulphate powder should be added on till the solution becomes saturated, i.e., no more powder can be dissolved. It is then filtered into a china dish and allowed to cool. The solution should be kept undisturbed. Slowly, the crystals of copper sulphate separate out.

Question 9.
Explain how painting of an iron gate prevents it from rusting?
Answer:
Painting of an iron gate prevents it from rusting because it cuts the direct contact of iron from the air and therefore there is no further exposure of iron to oxygen and moisture in the air which can cause rusting. Hence, rusting is prevented.

Question 10.
Explain why rusting of iron objects is faster in coastal areas than in deserts.
Answer:
Both the air and the moisture are required for rusting to take place. In coastal areas, the quantity of moisture present in the air is more than in deserts. In desert areas, the amount of moisture in the air is very low. Therefore, rusting of iron objects is faster in coastal areas than in deserts.

Question 11.
The gas we use in the kitchen is called liquefied petroleum gas (LPG). In the cylinder it exists as a liquid. When it comes out from the cylinder it becomes a gas (Change-A) then it burns (Change-B). The following statements pertain to these changes. Choose the correct one.
a. Process-A is a chemical change.
b. Process-B is a chemical change.
c. Both processes A and B are chemical changes.
d. None of these processes is a chemical change.
Answer:
b. Process-B is a chemical change.

Question 12.
Anaerobic bacteria digest animal waste and produce biogas (Change-A). The biogas is then burnt as fuel (Change-B). The following statements pertain to these changes. Choose the correct one.
a. Process-A is a chemical change.
b. Process-B is a chemical change.
c. Both processes A and B are chemical changes.
d. None of these processes is a chemical change.
Answer:
c. Both processes A and B are chemical changes.

NCERT Extended Learning Activities and Projects

Question 1.
Describe two changes that are harmful. Explain why you consider them harmful. How can you prevent them?
Hint:
Two changes which are harmful are:
a. Rusting of iron: When iron is left exposed to air it reacts with oxygen and water in the air to form a powdery substance called rust.
Rusting of iron is harmful as rust slowly eats away the iron leading to its considerable loss. Rusting can be prevented by oiling, polishing and painting.

b. Spoilage of food grains: Food grains get spoiled over a period of time. This causes a loss to us. It can prevented in the following ways:

Drying food grains before storage.
Keeping the food grains in safe, cool and dry place.
Spraying insecticides in godowns.
Cleaning and packaging of food grains before storage.

Question 2.
Take three glass bottles with wide mouths. Label them A, B, C. Fill about half of bottle A with ordinary tap water. Fill bottle B with water which has been boiled for several minutes, to the same level as in A. In bottle C, take the same boiled water and of the same amount as in other bottles. In each bottle put a few similar iron nails so that they are completely underwater. Add a teaspoonful of cooking oil to the water in bottle C so that it forms a film on its surface. Put the bottles away for a few days. Take out nails from each bottle and observe them. Explain your observations.

Hint:
In test tube B: Formation of rust will take place since air from the atmosphere will dissolve in boiled water as it is uncovered.
In test tube C: No rust formation will occur since only water is present. No air is present in it as oil cuts off supply of air.
By the above observations we conclude that both air and water are essential for rusting. If out of these one is missing, rusting will not take place.

Question 3.
Prepare crystals of alum.
Hint:
Prepare a supersaturated solution of alum in a beaker by dissolving the powdered alum in water. For this, take a beaker half filled with water on a stand and heat it till it starts boiling. Add alum slowly to this solution. Keep on adding alum until no more alum can be dissolved. Filter the warm solution into another beaker. Now keep the filtered solution in a water bath containing ice. Do not disturb the solution. Large crystals of solid alum will be formed at the base of beaker when solution cools down.

Question 4.
Collect information about the type of fuels used for cooking in your area. Discuss with your teacher/parents/ others which fuels are less polluting and why.
Hint:
The following types of fuels are used in our area:
a. Solid fuels: coal, dung cake, wood, etc.
b. Liquid fuel: Kerosene oil.
c. Gaseous fuel: LPG. LPG is a less polluting fuel.

Activity 1

Objective: To study the change in state of ice.
Materials Required: A piece of ice, glass/ plastic tumbler.
Procedure:

Take some ice in a glass or plastic tumbler.
Melt some portion of ice by placing the tumbler in the sun.
Now we have a mixture of ice and water.
Now place the tumbler in a freezing mixture.
The mixture becomes solid ice once again.

Observations: On heating the ice, it is converted into water and on freezing, it again changes into ice.
Conclusion: In this activity, solid changes into liquid and liquid changes back into solid. Thus, there is no change in the properties of water.

Activity 2

Objective: To study the change in state of water. Materials required: Water, beaker, Bunsen burner and a pan with handle.
Procedure:

Take some water and boil it in a beaker.
Water vapour rises from the surface of water.
Hold an inverted pan by its handle over the steam at some distance from the boiling water. You can also keep some ice cubes over the pan.
Observe the inner surface of the pan.

Observations: When the water heated, it is converted into steam. On cooling down, the steam it converted into water again.
Conclusion: In this activity, there is no change in the properties of water. No new substance is formed. So, the boiling of water to form steam is a physical change.

Chemical Properties: The internal properties of a substance which are not directly observable from outside are known as its chemical properties. For example, curd is a product of milk but the internal properties of milk and curd are completely different.

Chemical Change: These changes are the changes in which the composition and chemical properties of a substance get changed. In chemical changes, new substances are produced. These changes are permanent and irreversible. For example, burning of a candle, formation of curd from milk, ripening of fruits, rusting of iron and silver jewellery getting tarnished or copper articles getting covered by green layer are all chemical changes.

Characteristics of Chemical Change:

A chemical change is a permanent change. It usually cannot be reversed by simple physical processes.
A lot of energy in the form of heat, light, etc., is either absorbed or given out in a chemical change.
A permanent change in colour may take place in a chemical change.
A change in smell or odour may take place or a new smell may be given off in a chemical change.
A gas may evolve in a chemical change.
A sound may also be produced in a chemical change.

Some examples of chemical changes are:
i. Burning: Burning of any substance such as coal, wood, etc., is always a chemical change and is accompanied by production of heat. When magnesium ribbon is burnt in air, it produces a dazzling white flame leaving behind ashes of magnesium oxide. When these ashes are dissolved in water, magnesium hydroxide (a base) is produced. Both these are chemical changes and can be represented as follows:
Magnesium (Mg) + Oxygen (O₂) → Magnesium oxide (MgO)
Magnesium oxide (MgO) + Water (H₂O) → Magnesium hydroxide [Mg(OH)₂]

Activity 3

Objective: To study burning of magnesium ribbon in air.
Materials Required: A magnesium ribbon, sand paper and candle.
Procedure:

Get a small piece of a thin strip or ribbon of magnesium.
Clean its tip with sandpaper.
Bring the tip near a candle flame.
Hold it for some time and observe.

Observations: It bums with a brilliant white light. When it is completely burnt, it leaves behind a powdery ash. It is called magnesium oxide.
Conclusion: Heat and light are given out in this process. It is not possible to recover magnesium ribbon in the original form from the white powdery ash. Therefore, burning of magnesium ribbon is a chemical change.

ii. Reaction of copper sulphate with iron is also a chemical change which represents a change is colour by formation of a new substance.

Activity 4

Objective: To study the reaction between copper sulphate solution and iron (iron nail/ shaving blade).
Materials Required: Test tube, copper sulphate, two glass beakers and an iron nail or a shaving blade.
Procedure:

Dissolve about a teaspoonful of copper sulphate (blue vitriol or neela thotha) in about half a cup of water in a glass tumbler or a beaker.
Add a few drops of dilute sulphuric acid to the solution. You should get a blue coloured solution.
Save a small sample of the solution in a test tube or a small glass bottle.
Drop an iron nail or a used shaving blade into the remaining solution.
Wait for half an hour or so. Observe the colour of the solution again.
Compare it with the colour of the sample solution saved separately.

Observations: Take out the nail or the blade. The changes that you noticed are due to a reaction between copper sulphate and iron. The change in colour of the solution from blue to green is due to the formation of iron sulphate, a new substance. The brown deposit on the iron nail is copper, another new substance. Conclusion: It can be said that iron reacts with copper sulphate to form iron sulphate and copper. The equation can be written as:
Copper sulphate solution (blue) + Iron → Iron sulphate solution (green) + Copper (brown deposit)

iii. Reaction between vinegar and baking soda is also a chemical change. Vinegar reacts with baking soda to produce carbon dioxide gas which turns lime water milky. The reaction can be represented as:
Carbon dioxide (CO₂) + Lime water [Ca(OH)₂] → Calcium carbonate [CaCO₃] (milky) + Water (H₂O)

Activity 5

Objective: To study the reaction between vinegar and baking soda.
Materials Required: Vinegar, baking soda, lime water, test tubes, rubber cork and delivery tube.
Procedure:

Fit one end of the delivery tube into a one-holed cork.
Fill one test tube with vinegar and add a pinch of baking soda to it.
Close the mouth of this tube with cork fitted with delivery tube.
Immerse the other end of the delivery tube into lime water as shown below.

Observation: Bubbles of gas are seen in vinegar. This gas turns lime water milky white in colour.
Conclusion: Carbon dioxide is released in the above reaction which turns lime water milky. It is a chemical change. The equation can be represented as:
Baking soda (NaHCO₃) + Vinegar (CH₃COOH) → Sodium acetate (CH₃COONa) + CO₂ + H₂O

Rusting of Iron: Iron reacts with oxygen and moisture present in the atmosphere to form a brown, flaky substance called rust. Rusting of iron is an undesirable change because the layer of rust formed falls off, exposing the metal to further rusting leading to corrosion of iron. As a result, iron objects become weak with passage of time. The process of rusting can be represented by the following equation:
Iron (Fe) + Oxygen (O₂) + Water (H₂O) → Iron oxide (Fe₂O₃.xH₂O)
The iron oxide is called rust. Rust of iron is chemically different from iron and hence rusting is a chemical change.

Methods to Prevent Rusting: Whenever you get iron, water and oxygen together, you get rust. So the best way to prevent rusting is to keep them apart. There are different methods to prevent rusting:

Painting: Painting the iron surface will create a barrier between the iron and the atmosphere which will protect the iron from rusting.
Oiling and Greasing: When the iron objects, such as machines, are coated with a thin layer of oil or grease, it prevents them to come in contact with moist air. Thus, rusting does not take place.
Galvanisation: Galvanisation is a process in which the iron sheets are coated with a layer of zinc which prevents rusting. Zinc gets oxidised more readily than iron. So, the iron remains protected. It is done in ships and many other articles.
Electroplating: Iron sheets can be electroplated with a metal which is more reactive than iron so that instead of iron getting oxidised, the other metal gets oxidised (because it is more reactive).
Alloying: Mixing of two or more metals or metals and non-metals is called alloying and the substance formed is called on alloy. It also prevents rusting. For example, stainless steel is on alloy of iron, carbon, chromium, nickel and manganese. It does not rust.

Crystallisation: Crystallisation is a technique used for the purification of substances. It is a separation technique to separate pure solids from a solution. Crystallisation is an example of a physical change. For example, common salt is obtained from seawater by evaporation and crystallisation. Similarly, when copper sulphate is dissolved in hot acidified water and then cooked, pure crystals of copper sulphate are obtained.

Class 7 Science Chapter 6 Physical and Chemical Changes Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What are the two main kinds of changes?
Answer:
Physical changes and chemical changes.

Question 2.
Which property of water changes during its evaporation?
Answer:
Physical property, i.e., state changes.

Question 3.
Is burning of a piece of paper a reversible or an irreversible change?
Answer:
It is an irreversible change.

Question 4.
What is rust?
Answer:
Iron reacts with oxygen and moisture present in the atmosphere to form a brown, flaky substance called rust. It is chemically iron oxide.

Question 5.
What kind of change is rusting?
Answer:
Chemical change.

Question 6.
What are the essential conditions for rusting?
Answer:
Presence of moisture and presence of oxygen in the air.

Question 7.
What is the nature of aqueous solution of magnesium oxide?
Answer:
When magnesium oxide is dissolved in water, it forms an aqueous solution which is basic in nature. The reaction between magnesium oxide and water is: Magnesium oxide (MgO) + Water (H₂O) → Magnesium hydroxide [Mg(OH)₂] In this reaction a new product is formed, which is magnesium hydroxide which is a base.

Question 8.
Give two examples of physical changes.
Answer:
Boiling of water, mixing sand and water.

Question 9.
Which type of change occurs during crystallisation?
Answer:
Physical change.

Question 10.
Which of the two is a permanent change-chemical change or physical change?
Answer:
Chemical change is a permanent change.

Question 11.
What is the colour of flame when magnesium is burnt?
Answer:
Dazzling white colour.

Question 12.
Name the gas released when baking soda is mixed with vinegar.
Answer:
Carbon dioxide.

Question 13.
What happens when carbon dioxide is passed through lime water?
Answer:
Lime water becomes milky due to the formation of calcium carbonate.

Question 14.
What is blue vitriol?
Answer:
Crystals of copper sulphate pentahydrate are blue in colour. So, solution of copper sulphate in water it is commonly known as blue vitriol.

Question 15.
Name any two methods by which rusting of iron can be prevented.
Answer:
Rusting of iron can be prevented by painting and by galvanisation.

Question 16.
Name the technique for obtaining pure sugar from sugar solution?
Answer:
Crystallisation.

Short Answer Type Questions

Question 1.
Define galvanisation.
Answer:
The process of depositing a coat of zinc layer on articles made of copper, iron other metals, which get corroded when exposed to moist air for long time is called galvanisation. For example: Iron bridges and ships can be protected from rusting by galvanising the iron using zinc.

Question 2.
Define crystallisation.
Answer:
Crystallisation is a process that separates a pure solid in the form of its crystals from a solution. The crystallisation method is used to purify solids. For example, the salt we get from seawater can have many impurities in it. To remove these impurities, the process of crystallisation is used.

Question 3.
What are physical changes?
Answer:
A physical change is a type of change in which the form of matter is altered but one substance is not transformed into another. The size or shape of matter may be changed, but no chemical reaction occurs. Physical changes are usually reversible. For example, melting of ice, formation of steam, etc., are physical changes.

Question 4.
What is a chemical change?
Answer:
A chemical change occurs when one substance is transformed into one or more new products via a chemical reaction. Most chemical changes are not reversible. They involve evolution of heat, light, sound or gas. For example, burning of paper, formation of curd, etc., are all chemical changes.

Question 5.
Write the characteristics of a physical change?
Answer:
The characteristics of a physical change are:

No new substance is formed in a physical change
A physical change is a temporary change. It can be easily reversed.
Very little energy (such as heat, etc.) is either absorbed or evolved in a physical change.
A temporary change in colour may take place in a physical change.

Question 6.
Why is vapourisation of water a physical change? Explain.
Answer:
Evaporation is a physical change and not a chemical change. It is a physical change because it is going from the liquid phase to the gas phase, i.e., the physical property is being changed. It is not a chemical change because its molecules are still made of two hydrogen atoms and an oxygen atom. Hence, no new substance is formed.

Question 7.
Does the energy change take place both in physical and chemical changes?
Answer:
Yes, all types of changes involve energy changes. During a change, energy is either evolved or absorbed. Burning of candle is a chemical change and energy is evolved in it. Evaporation of liquid is a physical change and energy is absorbed in it.

Question 8.
Write the characteristics of a chemical change?
Answer:
The characteristics of a chemical change are:

A chemical change is a permanent change. It usually cannot be reversed.
A lot of energy in the form of heat, light, etc., is either absorbed or given out in a chemical change.
A permanent change in colour may take palace in a chemical change.
A change in smell may take place in a chemical change
A new substance is always formed in a chemical change.
Sound may be produced or a gas may evolve in a chemical change.

Question 9.
What happens when iron nails are dipped in copper sulphate solution?
Answer:
When iron nails are dipped in copper sulphate solution, then after some time a brown layer of copper gets deposited on iron nails. This change is due to the chemical reaction between copper sulphate solution and iron. The colour of copper sulphate solution also changes from blue to green colour due to the formation of iron sulphate.
Iron nail + Copper sulphate solution (Blue) → Iron sulphate (Green) + Copper (Brown deposit)

Question 10.
Ozone acts as a natural shield against ultraviolet radiations. Explain.
Answer:
Ozone protects us from the harmful ultraviolet radiations which come from the sun. Ozone absorbs this radiation and breaks down to oxygen. If ultraviolet radiations were not absorbed by ozone, it would reach the earth’s surface and cause harm to us and other life forms.

Question 11.
Is burning always a desirable change? Explain.
Answer:
No, it is not always a desirable change. It is desirable during cooking of food, burning of candle, burning of fossil fuels to drive engines and other machines. However, it is undesirable at other times as it causes a lot of damage, e.g., forest fire causes lot of damage to plants, animals and our ecosystem. Therefore, it is not always a desirable change.

Question 12.
State the reason for each of the following:
a. Cooked food is stored in a refrigerator.
b. Common salt is stored in an airtight container during the rainy season.
Answer:
a. Low temperature in a refrigerator slows down the growth and multiplication of microorganisms. This prevents the cooked food from spoilage.
b. Common salt absorbs moisture and becomes wet during rainy season. Therefore, to keep common salt dry (free flowing), it is stored in an airtight container during the rainy season.

Long Answer Type Questions

Question 1.
State four differences between physical and chemical changes.
Answer:

Physical change	Chemical change
1. No new substance is formed.	1. New substance is formed.
2. Only physical state and physical properties of the substance are changed.	2. The physical as well as chemical properties of the substance are changed.
3. It is a temporary change.	3. It is a permanent change.
4. Change is generally reversible.	4. Change is generally irreversible.
5. Example: Change of water into ice.	5. Example: Burning of paper.

Question 2.
State whether each of the following changes is slow/fast, reversible/ irreversible, desirable/undesirable or physical/chemical.
a. Rusting of iron
b. Melting of ice
c. Lighting of bulb
d. Growth of tree
e. Curdling of milk
Answer:
a. Rusting of iron is a slow, undesirable, irreversible and chemical change.
b. Melting of ice is a fast, undesirable, reversible and physical change.
c. Lighting of bulb is a fast, desirable, reversible and physical change.
d. Growth of tree is a slow, desirable, irreversible and chemical change.
e. Curdling of milk is a slow, desirable, irreversible and chemical change.

Question 3.
Why are chemical changes important in our daily lives?
Answer:
Chemical changes are very important in our lives because all new substances are formed as a result of chemical changes. For example, if a metal is to be extracted from an ore, such as iron from iron ore, we need to carry out a series of chemical changes. A medicine is the end product of a chain of chemical reactions. Useful new materials, such as plastics and detergents, are produced by chemical reactions. Indeed, every new material is discovered by studying chemical changes.

Question 4.
Which gas is released when vinegar and baking soda are mixed? What happens when this gas is passed through lime water?
Answer:
When baking soda and vinegar are mixed with each other, carbon dioxide gas is released. When carbon dioxide is passed through lime water, calcium carbonate is formed. Calcium carbonate, makes lime water appear milky. The turning of lime water into milky solution is a standard test of carbon dioxide. The following reactions take place:
a. Vinegar + Baking soda → Carbon dioxide + Other substance
b. Carbon dioxide (CO₂) + Lime water [Ca(OH₂)] → Calcium carbonate (CaCO₃) + Water (H₂O)

Question 5.
What is rusting? How do we prevent rusting?
Answer:
Iron reacts with oxygen and moisture present in the atmosphere to form a brown, flaky substance called rust. Rust of iron is undesirable because the layer of rust formed falls off, exposing the metal to further rusting. As a result, iron objects become weak with the passage of time.
Iron (Fe) + oxygen (O₂) + water (H₂O) → Iron oxide (Fe₂O₃.xH₂O)
The iron oxide is rust.

Methods to prevent rusting:

Putting oil or paint over the surface of iron articles.
By the process of galvanisation.
By electroplating.
By using anti-rust solution.

Question 6.
Identify the type of change and state whether energy is absorbed or evolved in each one of the following events: Burning of a candle, lighting of a bulb, preparation of food by green plants, volcanic eruption, lightning.
Answer:

S. No	Event	Type of Change	Energy absorbed or evolved
1.	Burning of a candle	Chemical change	Energy is evolved in the form of heat and light
2.	Lightning of a bulb	Physical change	Energy is evolved in the form of heat and light.
3.	Preparation of food by green plants	Chemical change	Energy is absorbed by chlorophyll from the sun.
4.	Volcanic eruption	Chemical change	Energy is evolved in the form of heat and light.
5.	Lightning	Physical change	Energy is released in the form of light and sound.

Picture-Based Questions

Question 1.
Observe the following figure and answer the question that follow:

a. What does this figure show?
b. Name the gas released.
c. Write the effect of the gas on lime water.
d. Write the reaction involved in the second test tube.
Answer:
a. This figure shows the reaction of acetic acid with baking soda.
b. The gas is carbon dioxide.
c. The lime water becomes milky.
d. Lime water [Ca(OH)₂] + Carbon dioxide (CO₂) → Calcium carbonate (CaCO₃) (milky) + Water (H₂O)

Question 2.
Identify the changes shown below and state in each case, whether it is a physical or a chemical change

Answer:
a. Rolling of dough into Chapati – physical change.
b. Cooking of Chapati – chemical change.
c. Melting of ice – physical change.
d. Burning of paper – chemical change.