Revision Notes for Class 7 Science Chapter 5: Changes Around Us – Physical and Chemical

Quick revision notes summarizing all key concepts from Class 7 Science Chapter 5 “Changes Around Us: Physical and Chemical”. These Class 7 Science Chapter 5 notes are ideal for quick revision just before exams.

• A physical change only alters the shape, size, or state of a substance; no new substance is formed, and it is often (but not always) reversible.
• A chemical change forms one or more new substances with different properties; it is generally irreversible.
• Reversible changes can be undone to recover the original substance (e.g., melting ice, dissolving sugar in water, boiling water). Irreversible changes cannot be undone (e.g., rusting, burning, ripening, cooking).
• Combustion is a chemical process where a substance reacts with oxygen and releases heat. It requires three things: a combustible substance (fuel), oxygen, and the substance reaching its ignition temperature.
• Ignition temperature is the minimum temperature at which a substance catches fire.
• Some processes (like burning a candle) involve both physical change (melting/evaporating wax) and chemical change (burning wax vapour) happening together.
• Rusting of iron and curdling of milk are classic examples of chemical changes forming new substances (iron oxide; curd).
• Magnesium oxide (formed when magnesium burns) is basic in nature; burning magnesium is a chemical change.
• Lime water (calcium hydroxide solution) turns milky when carbon dioxide gas is passed through it, forming calcium carbonate — a standard test for CO2.
• Soil formation from rocks involves both physical weathering (breaking rocks into smaller pieces) and chemical weathering (altering mineral composition).

NCERT Solutions: Class 7 Science Chapter 5
Extra Questions: Class 7 Science Chapter 5

For the full chapter, see the Class 7 Science book page and the Class 7 Science Formulas Handbook.

Written by Satish

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