Class 7 Science - UP
Changes Around Us: Physical and Chemical
In the Class 7 Science chapter 'Changes Around Us: Physical and Chemical', students explore the various changes happening in daily life, such as melting ice, boiling water, rusting of iron, and burning paper. This chapter is crucial for UP Board exams as it builds the foundational understanding of matter, distinguishing between reversible and irreversible changes, and temporary and permanent changes. Scoring well in this chapter depends on clearly differentiating between physical properties and chemical reactions, which frequently appear in both objective and descriptive board exam 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. These changes are usually reversible.
Chemical Change
A change in which one or more new substances with entirely different properties are formed. These changes are permanent and generally irreversible.
Reversible Change
A change that can be undone or reversed to get back the original substance, such as freezing of water into ice and melting of ice back to water.
Irreversible Change
A change that cannot be undone to recover the original substance, such as burning a piece of paper or cooking food.
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 UP Board Class 7 Science examinations, this chapter typically carries around 5 to 8 marks. Common question types include fill-in-the-blanks, multiple-choice questions (MCQs), short answer questions distinguishing between physical and chemical changes, and reasons for phenomena like why rusting happens faster in coastal areas.
Frequently Asked Questions
Is melting of wax a physical or chemical change?
Melting of wax is generally a physical change because the molten wax solidifies back into wax on cooling. However, burning of candle 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?
We can prevent rusting by applying a layer of paint or grease, or by coating iron with a layer of a non-rusting metal like zinc (galvanization).
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