Chapter 6 – Physical and chemical changes

These NCERT Class 7 Science Chapter 6 notes explain different types of changes that occur around us in daily life. The chapter helps students understand that some changes are temporary while others are permanent, and why this difference is important in science.

Physical and Chemical Changes clearly explains how physical changes differ from chemical changes using simple examples like melting of ice and rusting of iron. The chapter also introduces rusting, its causes, and methods to prevent it.

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1. Introduction: why changes matter

•  Changes occur around us all the time in daily life.
•  Some changes are temporary, while others are permanent.
•  Studying changes helps us understand how substances behave.
•  Ice melting and iron rusting may look similar but are very different.

2. What is a change

•  A change means an alteration in shape, size, state, or composition.
•  Changes are broadly classified as physical or chemical.

3. Physical change

•  A physical change is a change in which no new substance is formed.
•  Physical changes are usually reversible.
•  Melting of ice, breaking of glass, and stretching rubber are examples.

4. Characteristics of physical changes

•  No new substance is formed during a physical change.
•  Only shape, size, or state changes.
•  Physical changes are mostly reversible.
•  Chemical composition remains the same.

5. Changes in state

•  Matter can change from solid → liquid → gas.
•  These changes occur due to heating or cooling.
•  Ice, water, and steam show change of state.

6. Expansion and contraction

•  Substances expand on heating and contract on cooling.
•  Heating causes particles to move farther apart.
•  A metal lid loosens when heated due to expansion.

7. Chemical change

•  A chemical change forms one or more new substances.
•  Chemical changes are usually irreversible.
•  Burning paper, rusting iron, and cooking food are examples.

8. Characteristics of chemical changes

•  A new substance is always formed.
•  Chemical changes are permanent.
•  Chemical composition changes completely.
•  Energy change occurs during the process.

9. Rusting of iron

•  Rusting is a chemical change of iron.
•  It occurs when iron reacts with oxygen and water.
•  Rust is a reddish-brown substance called iron oxide.

10. Conditions required for rusting

•  Air (oxygen) must be present for rusting.
•  Water (moisture) is also necessary.
•  Rusting does not occur if either air or water is absent.

11. Prevention of rusting

•  Painting prevents contact with air and water.
•  Greasing or oiling protects iron surfaces.
•  Galvanisation coats iron with zinc.
•  Chrome plating gives protection and shine.

12. Chemical changes in daily life

•  Digestion of food is a chemical change.
•  Respiration involves chemical reactions in the body.
•  Curd formation from milk is a chemical change.

13. Reversible and irreversible changes

•  A reversible change can be undone, like melting of ice.
•  An irreversible change cannot be undone, like burning paper.

14. Physical vs chemical change

•  Physical change does not form a new substance and is usually reversible.
•  Chemical change forms a new substance and is usually irreversible.

15. Important keywords with simple definitions

•  Physical change – change with no new substance formed.
•  Chemical change – change that forms a new substance.
•  Rusting – slow reaction of iron with air and water.
•  Galvanisation – coating iron with zinc to prevent rusting.
•  Reversible – change that can be undone.
•  Irreversible – change that cannot be undone.

Understanding NCERT Class 7 Science Chapter 6 – Physical and Chemical Changes is important to identify how substances change in everyday life. The chapter helps students distinguish between reversible and irreversible changes and understand the science behind rusting.

These concepts are frequently asked in school examinations and are useful for foundation-level science preparation. Students should next read Chapter 7: Weather, Climate and Adaptations of Animals to Climate to understand environmental conditions and survival of animals.

FAQs

Q1. What is explained in NCERT Class 7 Science Chapter 6?
The chapter explains physical changes, chemical changes, rusting, and types of changes.

Q2. What is a physical change?
A physical change is a change in which no new substance is formed.

Q3. What is a chemical change?
A chemical change is a change in which one or more new substances are formed.

Q4. What is rusting of iron?
Rusting is a chemical change in which iron reacts with air and moisture to form rust.

Q5. Why is NCERT Class 7 Science Chapter 6 important for exams?
It explains basic concepts of changes in matter, which are commonly asked in school and foundation-level exams.

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