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CBSE - VII
Physical and Chemical Changes
Physical and Chemical Changes
All changes that you see can be broadly divided into physical and chemical changes
Lesson Demo
Chemical change is a permanent change in which new substances are formed with different properties along with the evolution or absorption of some kind of energy.
Some examples for chemical change are:
- Rusting of iron, as rust cannot be converted back into iron by physical means.
- Burning of fuels like petrol, kerosene, diesel, wood, charcoal and coal.
- Digestion of food by living organisms.
- Photosynthesis in plants.
- Butter turning rancid (sour).
- Fermentation of sugarcane juice and fruit juice.
- Charring of sugar into charcoal on strong heating.
It is important to note that when a chemical change occurs in a substance, then we can say that a chemical reaction has taken place.
For example:
- The metals that we use in our everyday life are obtained from their ores by carrying out a series of chemical reactions.
- All kinds of plastics are prepared by chemical reactions.
- New medicines are produced by a series of chemical reactions.
- All kinds of building materials are prepared by chemical reactions.
