Class 7 Science - ODISHA
Changes Around Us: Physical and Chemical
The chapter 'Changes Around Us: Physical and Chemical' explores the various transformations occurring in our daily lives, distinguishing between temporary changes where no new substances are formed and permanent changes where new substances with different properties are created. Students in Class 7 under the Odisha Board (BSE) will learn to identify examples like melting ice, boiling water, rusting of iron, and burning of magnesium. Understanding these concepts is fundamental for board exams as it builds the scientific foundation for chemistry, helping students differentiate between reversible and irreversible processes through practical observations.
Start Learning FreeKey Concepts
Physical Change
A change in which only the physical properties of a substance like shape, size, color, or state change, and no new substance is formed. These changes are mostly reversible.
Chemical Change
A change in which one or more new substances with entirely different chemical properties are formed. These changes are permanent and usually irreversible.
Crystallization
The process of obtaining pure crystals of a substance from its saturated solution. It is a physical change used commonly in purifying salts like common salt from sea water.
Rusting of Iron
A chemical process where iron reacts with oxygen and moisture present in the air to form a reddish-brown coating called rust (iron oxide).
Galvanization
A method of protecting iron from rusting by coating it with a thin layer of a non-reactive metal like zinc.
Important Formulas
Board Exam Info
In the Odisha (BSE) Class 7 Science examinations, this chapter typically carries around 4 to 6 marks. Common question types include short-answer questions differentiating between physical and chemical changes, reasons for why rusting occurs, and identifying whether given daily life examples are physical or chemical changes.
Frequently Asked Questions
Is tearing paper a physical or chemical change?
Tearing paper is a physical change because only the size and shape of the paper change, and no new chemical substance is formed.
Why is burning a candle considered both a physical and chemical change?
Melting of wax is a physical change because the melted wax can solidify again, while the burning of wax vapor produces heat, light, carbon dioxide, and water vapor, which is a chemical change.
How can we prevent iron from rusting?
Iron can be prevented from rusting by painting, greasing, oiling, or by coating it with a layer of zinc through a process called galvanization.
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