Class 7 Science - TELANGANA
Changes Around Us: Physical and Chemical
The Telangana (TSBSE) Class 7 Science chapter 'Changes Around Us: Physical and Chemical' explores the various transformations occurring in our daily lives, such as melting ice, rusting iron, and burning paper. Students learn to classify these changes into physical changes, where no new substances are formed and changes are often reversible, and chemical changes, where new substances are formed and changes are permanent. Understanding this distinction is crucial for explaining natural phenomena, industrial processes, and holds high weightage in school examinations for testing conceptual clarity and real-world application.
Start Learning FreeKey Concepts
Physical Change
A change in which only the physical properties of a substance like shape, size, color, or state change, without forming any new substance.
Chemical Change
A change in which one or more new substances with entirely different properties are formed, often accompanied by heat, light, or sound.
Reversible Change
A change that can be undone to get back the original substance, such as melting of ice or freezing of water.
Irreversible Change
A permanent change that cannot be undone to recover the original substance, such as burning of paper or cooking food.
Rusting of Iron
A chemical change where iron reacts with oxygen and moisture in the air to form a reddish-brown flaky layer called rust (iron oxide).
Crystallization
A physical process used to obtain pure crystals of a substance from its solution, such as obtaining salt crystals from sea water.
Important Formulas
Board Exam Info
In the Telangana (TSBSE) Class 7 Science examinations, this chapter typically carries about 4 to 6 marks. Common question types include 1-mark objective questions, 2-mark definitions, and 4-mark descriptive questions involving the classification of various daily life events into physical and chemical changes.
Frequently Asked Questions
Is dissolving sugar in water a physical or chemical change?
It is a physical change because no new substance is formed, and you can get the sugar back by evaporating the water.
Why is burning of a candle considered both a physical and chemical change?
Melting of wax is a physical change because solid wax changes to liquid and back. However, the burning of wax vapor produces carbon dioxide, heat, and light, which is a chemical change.
How can we prevent iron from rusting?
We can prevent rusting by applying a coat of paint, grease, or by the process of galvanization (depositing a layer of zinc on iron).
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