Physical and Chemical Changes Class 7 Science Part 1 Chapter 6

Free Solutions for Assam State Board Class 7 Science Chapter 6 in English Medium

Physical and Chemical Changes Questions and Answers Class 7 Science Part 1 Chapter 6 Assam State Education Board Syllabus 2025-2026 Covered

Physical and chemical changes are fundamental concepts in science that help us understand the transformations of matter. Below are the important questions and answers from NCERT & SCERT Assam Class 7 Science Chapter 6 - Physical and Chemical Changes, based on the Assam State Education Board syllabus for 2025-2026.

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Introduction to Physical and Chemical Changes

A physical change is a change in the form or appearance of a substance without altering its chemical composition. A chemical change, on the other hand, results in the formation of a new substance with different properties.

Class 7 Science Question Answer – Part I All Chapters

Below are the chapters of Class 7 Science. Click on the chapter name to access the respective question-and-answer content:

1. Nutrition in Plants
2. Nutrition in Animals
3. Heat
4. Motion and Time
5. Acids, Bases and Salts
6. Physical and Chemical Changes
7. Weather, Climate and Adaptations of Animals to Climate
8. Winds, Storms and Cyclones
9. Soil

 

 

Physical and Chemical Changes

 

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

Ans:-

a) Chemical change

b) Physical Change

c) Chemical change

d) Physical Change

e) Physical Change

f) Chemical change

 

 

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. (True/False)

(b) Formation of manure from leaves is a physical change. (True/False)

(c) Iron pipes coated with zinc do not get rusted easily. (True/False)

(d) Iron and rust are the same substances. (True/False)

(e) Condensation of steam is not a chemical change. (True/False)

Ans:-

a) False

b) False

c) True

d) False

e) True

 

 

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.

Ans:-

(a) When carbon dioxide is passed through lime water, it turns milky due to the formation of Calcium carbonate.

(b) The chemical name of baking soda is Sodium hydrogen carbonate.

(c) Two methods by which rusting of iron can be prevented are painting and galvanisation.

(d) Changes in which only physical properties of a substance change are called physical changes.

(e) Changes in which new substances are formed are called chemical changes.

 

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.

Ans:-     When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a carbon dioxide gas. This is a chemical change.

Lemon juice + Baking soda → Carbon dioxide + other substances.

 

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 chemical and physical changes take place.

Ans:-

(i)                 Candle Burning

(ii)               Physical change is the melting of the wax.

(iii)             The chemical change is the burning of gas with the evolution of CO₂.

(iv)             Digestion of Food.

(v)               Physical change is the breakdown of larger food molecules into simpler ones.

(vi)             The chemical change is the digestion of food by the action of HCl and enzymes.

 

 

6. How would you show that the setting of curd is a chemical change?

Ans:-       The setting of curd is a chemical change because curd cannot be turned back to milk. The properties of milk and curd are different.

 

7. Explain why burning wood and cutting it into small pieces are considered two different types of changes.

Ans:- Cutting wood is a physical change as it does not change the nature of the wood. On the other hand, the burning of wood is a chemical change as wood is converted to charcoal with the liberation of CO₂.

 

8. Describe how crystals of copper sulphate are prepared.

Ans:-   Crystals of copper sulphate are prepared using the crystallisation method, which is described as follows:

Take a cupful of water in a beaker.

Add a few drops of dilute sulphuric acid to this.

Heat the water, and when it starts boiling, add copper sulphate powder while still stirring.

Add the copper sulphate powder till the solution becomes saturated. Filter into a china dish and allow it to cool.

The solution should be kept undisturbed. Slowly, the crystals of copper sulphate separate out.

 

 

9. Explain how painting an iron gate prevents it from rusting.

Ans:-     Rusting of iron requires contact with water (moisture) and oxygen. By painting an iron gate, we prevent contact between iron, Oxygen and water (moisture); this helps in preventing rusting of iron.

 

10. Explain why rusting of iron objects is faster in coastal areas than in deserts.

Ans:-    Rusting of iron requires contact with water (moisture) and oxygen. In coastal areas, humidity is more in comparison to that in deserts; hence, rusting of iron objects is faster in coastal areas than in deserts.

 

11. The gas we use in the kitchen is called liquified 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.

(i) Process – A is a chemical change.

(ii) Process – B is a chemical change.

(iii) Both processes A and B are chemical changes.

(iv) None of these processes is a chemical change.

Ans:-  The answer is (ii) Process – B is a chemical change.

 

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.

(i) Process – A is a chemical change..

(ii) Process – B is a chemical change

(iii) Both processes A and B are chemical changes.

(iv) None of these processes is a chemical change.

Ans:-  The answer is (iii) Both processes A and B are chemical changes. 

 

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Class 7 Science Chapter 6 - Important Questions & Answers

Q1: What is a physical change? Give an example.

Answer: A physical change is a change in the shape, size, or state of a substance without forming a new substance. Example: Melting of ice into water.

Q2: What is a chemical change? Give an example.

Answer: A chemical change is a process where one or more substances react to form new substances with different properties. Example: Rusting of iron.

Q3: How is a physical change different from a chemical change?

Difference Between Physical and Chemical Changes

Feature	Physical Change	Chemical Change
Formation of a new substance	No	Yes
Reversibility	Usually reversible	Irreversible
Example	Tearing of paper	Burning of paper

Q4: What are the characteristics of a chemical change?

Answer: A chemical change involves:

Formation of a new substance
Change in color
Evolution of gas
Release or absorption of heat

Q5: What is rusting of iron? How can it be prevented?

Answer: Rusting is the slow reaction of iron with oxygen and water, forming iron oxide (rust). It can be prevented by:

Painting or applying oil on iron objects
Galvanization (coating with zinc)
Using stainless steel

Q6: What is crystallization? Give an example.

Answer: Crystallization is the process of obtaining pure solid crystals from a solution. Example: Formation of salt crystals when seawater evaporates.

Q7: What happens when magnesium ribbon burns in air?

Answer: Magnesium burns in air to form magnesium oxide, a white powder. $\text{Mg} + \text{O₂} \rightarrow \text{MgO}$

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FAQs on Physical and Chemical Changes

Q1: Why is melting of wax a physical change but burning of wax a chemical change?

Answer: Melting of wax is a physical change because it changes state but remains wax. Burning of wax is a chemical change as it produces new substances like carbon dioxide and water vapor.

Q2: What happens when iron reacts with copper sulfate solution?

Answer: Iron displaces copper, forming iron sulfate and copper metal. $\text{Fe} + \text{CuSO₄} \rightarrow \text{FeSO₄} + \text{Cu}$

Q3: Is dissolving salt in water a physical or chemical change?

Answer: Dissolving salt in water is a physical change because no new substance is formed and it can be reversed by evaporation.

Q4: What are examples of chemical changes in daily life?

Answer:

Cooking of food
Digestion in the human body
Burning of fuels
Photosynthesis in plants

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