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Physical & Chemical Changes Summary Class 7 NCERT Summary

Types of Changes

  • Changes can broadly be classified into two types − physical and chemical.

Physical Change

  • Properties such as shape, size, colour and state of a substance are called its physical properties.
  • A physical change in which a substance undergoes a change in its physical properties is called a  physical change.

Chemical Change

  • A change in which one or more new substances are formed is called a chemical change.
  • A chemical change in which a substance undergoes a change in its chemical properties is called a chemical change.

Burning of Magnesium Ribbon

  • Magnesium ribbon burns with a brilliant white and leaves behind a powdery ash when completely burnt.
    Magnesium (Mg) + Oxygen (O2) → Magnesium oxide (MgO)

Dissolving magnesium ash in water

Magnesium oxide (MgO) + Water (H2O) → Magnesium hydroxide [Mg(OH)2]

Difference between Physical and Chemical Change

Physical & Chemical Changes Summary Class 7 NCERT Summary

  • Burning a candle is a combination of physical and chemical change.

Copper Sulphate Chemical Reaction

Physical & Chemical Changes Summary Class 7 NCERT Summary

  • When copper sulphate reacts with iron, the colour of the solution changes from blue to green due to the formation of iron sulphate.
  • Copper Sulphate solution (blue) + Iron → Iron Sulphate solution (green) + Copper (brown deposit)

Rusting

Physical & Chemical Changes Summary Class 7 NCERT Summary

  • Rusting is an example of chemical change.
    Iron (Fe) + Oxygen (O2, from the air) + water (H2O) → rust (iron oxide Fe2O3)
  • Presence of both air and water is essential for rusting to take place.
  • Rusting can be prevented by cutting the contact of either air or water or both with iron.

Protection from Rusting

  • The same can be done by greasing, oiling, painting, and galvanizing iron.
  • The process of depositing a layer of zinc on iron is called galvanization.
  • Rusting can also be checked by alloying iron with other elements. Stainless steel is an alloy of iron with carbon, chromium, nickel, and manganese.

Crystallization

  • Crystallization is an example of physical change. The process of crystallization is used for purification of some substances.

Physical & Chemical Changes Summary Class 7 NCERT Summary

The document Physical & Chemical Changes Summary Class 7 NCERT Summary is a part of the Class 7 Course NCERT Textbooks & Solutions for Class 7.
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FAQs on Physical & Chemical Changes Summary Class 7 NCERT Summary

1. What is a physical change?
Ans. A physical change is a type of change in which the form or appearance of a substance is altered, but its chemical composition remains the same. Examples of physical changes include melting ice, boiling water, and tearing a piece of paper.
2. What is a chemical change?
Ans. A chemical change, also known as a chemical reaction, is a process where one or more substances are transformed into new substances with different chemical properties. During a chemical change, the composition of the substances involved is altered. Examples of chemical changes include burning wood, rusting of iron, and digestion of food.
3. What are some differences between physical and chemical changes?
Ans. Some differences between physical and chemical changes include: - Physical changes only affect the physical properties of a substance, such as its shape, size, or state of matter, while chemical changes involve the formation of new substances. - In physical changes, the original substances can be easily reversed back to their original form, whereas in chemical changes, the original substances cannot be easily obtained again. - Physical changes do not involve the breaking or formation of chemical bonds, while chemical changes do. - Physical changes generally do not produce energy, while chemical changes often involve the release or absorption of energy.
4. What are some examples of physical changes?
Ans. Some examples of physical changes include: - Melting of ice: When ice melts, it changes from a solid to a liquid state without any change in its chemical composition. - Boiling water: When water is heated, it changes from a liquid to a gaseous state without any change in its chemical composition. - Crushing a can: When a can is crushed, its shape changes, but the material remains the same.
5. What are some examples of chemical changes?
Ans. Some examples of chemical changes include: - Burning wood: When wood is burned, it undergoes a chemical reaction with oxygen in the air, producing carbon dioxide, water vapor, and ash. - Digestion of food: When food is digested in our body, it undergoes a series of chemical reactions to break down complex molecules into simpler ones that can be absorbed and utilized by our cells. - Rusting of iron: When iron is exposed to oxygen and moisture, it undergoes a chemical reaction that forms iron oxide, commonly known as rust.
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