Class 7 Science - GUJARAT
Changes Around Us: Physical and Chemical
The chapter 'Changes Around Us: Physical and Chemical' in Class 7 GSEB Science introduces students to the daily transformations occurring in nature and our surroundings. Students learn to distinguish between reversible and irreversible changes, as well as temporary physical changes and permanent chemical changes. The chapter explores fascinating phenomena like crystallization, rusting of iron, and magnesium ribbon burning. Mastering this chapter is crucial for Gujarat Board exams as it builds the foundational concepts of chemistry, frequently appearing in conceptual, difference-based, and application-based questions.
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.
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 folding of paper.
Irreversible Change
A change that cannot be reversed to get back the original substance, such as cooking food or burning wood.
Rusting of Iron
A chemical process where iron reacts with oxygen and moisture present in the air to form a brown flaky layer called rust (iron oxide).
Crystallization
The process of obtaining pure crystals of a substance from its saturated solution, which is considered a physical change.
Important Formulas
Board Exam Info
In the Gujarat (GSEB) Class 7 Science examinations, this chapter typically carries around 4 to 6 marks. Questions usually include distinguishing between physical and chemical changes, giving reasons for processes like rusting or burning, and identifying examples of reversible and irreversible changes.
Frequently Asked Questions
Is melting of ice a physical or chemical change?
Melting of ice is a physical change because water only changes its state from solid to liquid, and no new substance is formed.
Why is digestion of food considered a chemical change?
Digestion is a chemical change because complex food substances are broken down into simpler new substances using digestive juices, and the original food cannot be recovered.
How can we prevent iron from rusting?
Iron can be prevented from rusting by painting, greasing, oiling, or applying a coating of a non-rusting metal like zinc or chromium (galvanization).
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