Important points of Physical and Chemical Changes | Class VI, VII and IX

1. A physical change is a temporary one which changes the physical appearance of a substance without changing its chemical composition.
2. A chemical change is a permanent change in which new and differ, substances having different composition and properties from those of original substances are formed.
3. The process of change of a substance from one physical state to another a definite temperature is called change of state.
4. The process in which a solid converts into liquid at a fixed temperature called melting.
5. The process of conversion of a liquid into its vapour at a fixed temperature called boiling.
6. The process in which a substance changes its state from a gas to a liquid a fixed temperature is called condensation.
7. The process in which a liquid converts into its solid state on cooling at fixed temperature is called freezing.
8. The process in which a solid directly changes into its gaseous state all temperatures is called sublimation.
The reverse process in which gas changes into solid on cooling is known as solidification.
9. The changes that involve absorption of energy are known as endothermic changes.
10. The changes that involve evolution or release of energy are known as exothermic changes.

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