Every substances changes in form or the other.
There are some cases when a new substance is formed , and there are some cases when a new substance is not formed.
These are called Physical and Chemical Changes, let's discuss them one by one
Physical Changes
Change in which no new substance is formed is called Physical Change.
These changes are
reversible
Example
- When ice melts into water , it is a physical change
- It is because ice and water are chemically same (both are H 2 O)
- Also we can convert ice back into water
-
Hence, this change is physical change.
Chemical Changes
Changes in which new substances are formed are Chemical Changes.
These changes are
normally irreversible
Example
- Burning is chemical change
- When a paper is burnt, it turns into carbon
- This change cannot be reversed to get back paper
- Hence, this change is chemical change.
Whether following are Physical Change or Chemical Change ?
1. Burning of Candle
Both Physical Change and Chemical change
- When a candle is burnt, its wax melts from solid to liquid and no new substance is formed, hence its a physical change.
- But the burning of the vapour is a chemical change.
2. Cutting of Trees
Physical change
- During cutting of trees no new substance is formed , hence its a physical change.
3. Rusting of Almirah (Rusting of Iron)
Chemical Change
- Rusting is a chemical reaction in which iron reacts with oxygen to form a new substance called rust (ferric oxide) , hence its a chemical change
4. Passing of Current in Water
Chemical Change
- Passing current in water breaks it into Hydrogen and Oxygen, hence new substances are formed . Therefore, its a chemical change
5. Making of Fruit Salad with Raw fruits
Physical Change
-
No new substances
are
formed
hence it is a Physical change.
6. Burning of Paper and Wood
Chemical Change
- When we burn paper and wood, new substances are formed like carbon and smoke
- This change cannot be reversed
7. Melting of Butter in pan
Physical change
- It is a change of state of matter from solid to liquid
- This change is temporary and can be reversed.
8. Dissolving of Salt in Water
Physical change
- The change can be reversed to get back salt and water
- This can be done by heating solution of salt and water
- Water will convert into water vapour and we can get salt at the bottom of container
9. Breaking of Glass Tumbler
Physical change
- No new substance is formed
- When a glass tumbler breaks, different pieces of broken glass are still same substance (glass)
10. Switching on of Electric Bulb
Physical change
- The change is temporary and can be reversed
- When bulb is switched on, the filament of bulb becomes hot and gives heat and light
- However when bulb is switched off, it turns back into original state
- Hence this change is temporary.
11. Heating of Magnesium Wire
Chemical Change
- It is a chemical change because a new substance is formed.
- When a magnesium wire is heated, it forms a new substance magnesium oxide which is a completely different substance from magnesium.
