Class 7 Science - RAJASTHAN
Changes Around Us: Physical and Chemical
In the chapter 'Changes Around Us: Physical and Chemical' for Class 7 Rajasthan Board Science, students explore the fascinating transformations that occur in our daily environment. The chapter distinguishes between temporary physical changes, where no new substance is formed, and permanent chemical changes, such as rusting and digestion, which result in new products. Understanding these concepts is crucial for board exams as it builds the foundational chemical reasoning required for higher classes. Students learn to identify characteristics like color change, gas evolution, and heat production, helping them score high in both conceptual and application-based questions.
Start Learning FreeKey Concepts
Physical Change
A change in which a substance undergoes a change in its physical properties like shape, size, color, or state, but no new substance is formed. These changes are mostly reversible.
Chemical Change
A change in which one or more new substances with entirely 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).
Crystallization
The process of obtaining large, pure crystals of a substance from its saturated solution. It is considered a physical change.
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 the Rajasthan Board Class 7 Science examination, this chapter typically carries around 4 to 6 marks. Common question types include differentiate between physical and chemical changes, identifying types of changes given in daily life scenarios, and explaining the conditions necessary for rusting along with preventive measures.
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. However, burning of wax is a chemical change.
Why is photosynthesis considered a chemical change?
Photosynthesis is a chemical change because plants use carbon dioxide and water in the presence of sunlight to produce completely new substances, which are glucose and oxygen.
How can we prevent iron from rusting?
Iron can be prevented from rusting by applying a layer of paint or grease, or through a process called galvanization, which involves coating the iron with zinc.
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