Class 7 Science - HARYANA
Changes Around Us: Physical and Chemical
The chapter 'Changes Around Us: Physical and Chemical' explores the various transformations we observe in our daily lives, distinguishing between temporary changes where no new substance is formed and permanent changes resulting in entirely new materials. Students learn about processes like melting, boiling, rusting, and crystallization. Understanding these concepts is crucial for the Haryana Board of School Education (BSEH) Class 7 Science exams as it forms the foundational building block for chemistry. Board exams frequently test this chapter through direct definitions, differentiation-based questions, and practical real-life examples from our surroundings.
Start Learning FreeKey Concepts
Physical Change
A change in which only the physical properties of a substance, such as 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 completely different properties are formed. These changes are usually permanent and irreversible.
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), weakening the metal over time.
Galvanization
A protective method of depositing a layer of zinc on iron or steel objects to prevent them from rusting and corrosion.
Crystallization
A physical process used to obtain pure crystals of a solid substance from its saturated solution by cooling or evaporating.
Important Formulas
Board Exam Info
In the Haryana Board (BSEH) 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, giving reasons (e.g., why rusting is a chemical change), and multiple-choice questions based on practical examples like burning of paper or melting of ice.
Frequently Asked Questions
Is melting of wax a physical or chemical change?
Melting of wax is primarily a physical change because only the state of the wax changes from solid to liquid, and it solidifies back on cooling. However, burning of wax candlewick is a chemical change.
Why does turning lime water milky on passing carbon dioxide considered a chemical change?
It is a chemical change because carbon dioxide reacts with lime water to form a completely new substance called calcium carbonate, which makes the water look milky.
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 another metal like zinc or chromium through processes like galvanization.
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