Chapter-Chapter 5. Changes Around Us–Physical and Chemical Science Curiosity class 7 in english Medium CBSE Notes

Chapter 5: Changes Around Us – Physical and Chemical

Definitions:

Change: A change is any alteration in the form, size, state, or composition of a substance.

Physical Change: A physical change is a change in which no new substance is formed and only physical properties are altered.

Chemical Change: A chemical change is a change in which a new substance is formed with different properties.

Reversible Change: A reversible change is a change that can be undone to get the original substance back.

Irreversible Change: An irreversible change is a change that cannot be undone.

Evaporation: Evaporation is the process of conversion of liquid into vapour.

Condensation: Condensation is the process of conversion of vapour into liquid.

Rusting: Rusting is a chemical change in which iron reacts with oxygen and moisture to form rust.

Quick Revision Points:

• Changes can be physical or chemical.
• Physical changes do not form new substances.
• Chemical changes form new substances.
• Physical changes are usually reversible.
• Chemical changes are usually irreversible.
• Burning, rusting, and cooking are chemical changes.
• Melting and freezing are physical changes.
• Evaporation and condensation are opposite processes.
• New substance formation is the key sign of chemical change.
• Chemical changes often involve heat, light, or gas.
• Changes are important in daily life and industries.

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