Class 7 Science - TAMILNADU
Changes Around Us: Physical and Chemical
The Class 7 Tamil Nadu Samacheer Kalvi Science chapter 'Changes Around Us: Physical and Chemical' explores the daily transformations happening in our environment. Students learn to classify these changes into two main categories: physical changes, which are temporary and do not form new substances, and chemical changes, which are permanent and result in the formation of entirely new substances with different properties. Understanding this distinction is crucial for board exams as it forms the foundation for advanced chemistry concepts, helping students analyze real-world phenomena like rusting, melting, and burning in theoretical and practical questions.
Start Learning FreeKey Concepts
Physical Change
A change in which only physical properties like shape, size, color, or state of a substance change, and no new substance is formed. These changes are mostly reversible.
Chemical Change
A change in which one or more new substances with completely different properties are formed. These changes are permanent and generally irreversible.
Reversible Change
A change that can be undone to get back the original substance, such as melting of ice or stretching a rubber band.
Irreversible Change
A change that cannot be reversed to get back the original substance, such as burning of paper or cooking food.
Rusting of Iron
A chemical process where iron reacts with oxygen and moisture in the air to form a reddish-brown layer of hydrated iron oxide, commonly known as rust.
Crystallization
A physical process used to obtain pure crystals of a dissolved substance from its solution, such as obtaining salt from sea water.
Important Formulas
Board Exam Info
In the Tamil Nadu (Samacheer Kalvi) Class 7 Science examinations, this chapter typically carries around 6 to 8 marks. Questions frequently appear as objective type (fill in the blanks, choose the best answer), short answers asking to differentiate between physical and chemical changes, and reasoning questions such as why rusting or digestion is considered a chemical change.
Frequently Asked Questions
Is melting of ice a physical or chemical change?
It is a physical change because only the state changes from solid to liquid, and no new substance is formed. It is also reversible.
Why is burning of paper a chemical change?
Burning produces new substances like ash, carbon dioxide, and water vapor, which cannot be reversed to get back the original paper.
Is ripening of fruit a reversible change?
No, ripening of fruit is an irreversible and chemical change because a ripe fruit cannot be turned back into a raw fruit.
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