Class 7 Science - MP
Changes Around Us: Physical and Chemical
The chapter 'Changes Around Us: Physical and Chemical' explores the daily transformations we observe in our environment, categorizing them into physical and chemical changes. Students learn that physical changes are temporary and do not form new substances, such as melting ice or tearing paper. In contrast, chemical changes involve the formation of entirely new substances with different properties, like rusting of iron or burning wood. Understanding these differences is crucial for Class 7 MP Board exams, as questions frequently test the ability to identify change types and write balanced chemical word equations.
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 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 in the air to form a brown, flaky coating called rust, weakening the iron object over time.
Crystallization
A physical process used to obtain pure crystals of a substance from its saturated solution, such as obtaining pure salt crystals from sea water.
Galvanization
A method of protecting iron from rusting by coating it with a thin layer of a more reactive metal like zinc.
Important Formulas
Board Exam Info
In MP Board Class 7 Science examinations, this chapter typically carries around 6 to 8 marks. Common question types include short-answer questions differentiating between physical and chemical changes, fill-in-the-blanks, and reasoning questions such as why rusting is a chemical change.
Frequently Asked Questions
Is melting of wax a physical or chemical change?
Melting of wax is generally considered a physical change because only the state of the wax changes from solid to liquid, and it solidifies back on cooling. However, burning the wick of a candle is a chemical change.
Why does lime water turn milky when carbon dioxide is passed through it?
Carbon dioxide reacts with lime water (calcium hydroxide) to form a white precipitate of calcium carbonate, which makes the solution turn milky.
Can all physical changes be reversed?
Most physical changes are reversible, but not all. For example, tearing a piece of paper into small bits is a physical change, but it cannot be reversed to get the original sheet back.
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