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Physical and Chemical Changes

Gujarat Board · Class 7 · Science

Quick revision notes for Physical and Chemical Changes — Gujarat Board Class 7 Science. Key concepts, formulas, and definitions for last-minute revision.

42 questions5 concepts

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A labeled diagram showing the experimental setup for burning a magnesium ribbon in air and collecting the resulting magnesium oxide ash in a watch glass.
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Key Topics to Revise

1

Physical Changes

  • A physical change is a change in which only the physical properties of a substance change — such as shape, size, colour, or state.
  • No new substance is formed in a physical change.
  • Physical changes are generally reversible — the original substance can usually be recovered.
2

Chemical Changes

  • A chemical change is a change in which one or more new substances are formed.
  • A chemical change is also called a chemical reaction.
  • Chemical changes are generally irreversible — the original substance cannot be easily recovered.
3

Rusting of Iron and Its Prevention

  • Rusting is a chemical change in which iron reacts with oxygen and water to form rust (iron oxide, Fe₂O₃).
  • Both oxygen and water (or moisture) are essential for rusting. If either is absent, rusting does not occur.
  • High humidity (moisture in air) makes rusting faster.
4

Crystallisation

  • Crystallisation is the process of forming large, pure crystals of a substance from its solution.
  • It is a physical change because no new substance is formed — only the physical form changes.
  • Salt obtained from evaporation of sea water is not pure, but crystallisation gives pure, large, well-shaped crystals.

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Full Notes

Key Concepts

A physical change is a changeA chemical change is a changePhysical properties are characteristics ofChemical changes are often accompanied byRusting is a chemical change

Frequently Asked Questions

What are the important topics in Physical and Chemical Changes for Gujarat Board Class 7 Science?
Key topics in Physical and Chemical Changes include Chapter Overview: Physical and Chemical Changes, Physical and Chemical Changes – Complete Chapter Overview, Distinguishing Physical and Chemical Changes. These are the concepts Gujarat Board Class 7 examiners draw on most — study them first, then practise related questions.
How to score full marks in Physical and Chemical Changes — Gujarat Board Class 7 Science?
Understand the core concepts first, then work through the 42 practice questions available for this chapter. Revise formulas and definitions regularly, and use flashcards for quick recall before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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