Physical and chemical change of Class 7
Any change which can alters some physical property of the matter such as its state, texture, magnetic or electrical conditions or its colour, without causing any change in the composition of its molecules, is called physical change, or you can say it is a temporary change which can be easily reversed and in which only the physical properties of a substance change without any change in its composition. “Properties such as shape, size, colour and state of a substance are called physical properties. A change in which a substance undergoes a change in its physical properties is called a physical Change.
Following points need special consideration:
- Physical change is reversible and temporary.
- The composition of the substance does not change during a physical change and hence, no new substance is formed.
- No loss or gain of energy takes place during a physical change. The energy needed to bring about a physical change is equal to energy that can reverse the change. For example, 2260 J of heat energy is needed to change 1 g of water at 100°C to 1g of steam at 100°C. The same amount of heat energy is given out when 1g of steam condenses to 1 g of water at 100°C.
- No change in mass occurs during a physical change. This is because the substance undergoing a change remains the same. No matter is added or removed.
Examples of physical change:
- Making of ice-cream
- Boiling water into steam.
- Crystallization of sugar from its solution,
- Sublimation of camphor.
- Bending of glass tube by heating.
- Melting of wax.
- Evaporation of water.
- Glowing of an electric bulb
- Magnetising an iron bar by means of electricity.
- Dissolving sodium chloride in water
Some Examples Involving Physical Changes:
- Physical Changes
- Chemical Change
- Chemical Equations
- Change Of Physical State
- Difference between Physical and Chemical Changes
- Change Of Colour
- Formation Of Precipitate
- Rusting of Iron
- Energy Changes
- Mind Map
- solved questions