Class 7 Science - BIHAR
Changes Around Us: Physical and Chemical
The chapter 'Changes Around Us: Physical and Chemical' for Class 7 Bihar Board Science introduces students to the various changes occurring in their daily environment. Students will learn to distinguish between reversible and irreversible changes, and more importantly, between physical changes (where no new substance is formed) and chemical changes (where new substances with different properties are formed). Understanding these concepts is vital as they form the foundation for chemistry and general science. This chapter frequently features in Bihar Board annual examinations through objective questions, short-answer definitions, and practical examples like rusting and crystallization.
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.
Chemical Change
A change in which one or more new substances with entirely different chemical properties are formed, often accompanied by heat, light, or sound.
Reversible Change
A change that can be reversed 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 burning of paper or cooking of food.
Rusting of Iron
A chemical process where iron reacts with oxygen and moisture in the air to form a reddish-brown coating called rust (Iron oxide).
Crystallization
A physical process used to obtain pure crystals of a solid substance from its saturated solution, such as obtaining salt from sea water.
Important Formulas
Board Exam Info
In the Bihar Board Class 7 Science examination, this chapter typically carries around 4 to 6 marks. Questions usually include multiple-choice questions (MCQs), matching types, and short descriptive questions asking to classify given everyday occurrences into physical or chemical changes.
Frequently Asked Questions
Is melting of wax a physical or chemical change?
Melting of wax is primarily a physical change because the melted wax can solidify again on cooling. However, if the wax burns, that burning part is a chemical change.
Why is ripening of fruit considered a chemical change?
Ripening of fruit is a chemical change because the fruit changes its color, taste, and texture, and new substances are formed which cannot be turned back into the raw fruit.
How can we prevent rusting of iron?
Rusting can be prevented by applying a layer of paint, grease, oil, or by the process of galvanization (coating iron with a layer of zinc).
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