A physical change is a change in which only the physical properties of a substance, such as shape, size, or state, are altered and a chemical change is a change in which the chemical composition of a substance changes, resulting in the formation of one or more new substances with different properties.
Example:
- Physical changes: melting of ice, boiling of water, cutting paper
- Chemical changes: rusting of iron, burning of wood, cooking of food
Physical Change
A physical change is a change in which only the physical properties of a substance (such as shape, size, or state) change, and no new substance is formed.
Example:
- Melting of ice
- Boiling of water
- Freezing of water
- Cutting or tearing of paper
- Breaking of glass
Characteristics of Physical Change
The important characteristics of a physical change are:
- No new substance is formed: The substance remains the same before and after the change.
- Only physical properties change: Properties such as shape, size, state, volume, or appearance may change.
- Chemical composition remains unchanged: The molecules of the substance remain the same.
- Usually reversible: Many physical changes can be reversed to obtain the original substance.
- Small energy change: Only a small amount of energy is absorbed or released, mainly during change of state.
- No chemical reaction occurs: The change does not involve breaking or forming of chemical bonds.
- Only arrangement of particles changes: The particles remain the same, but their arrangement or distance may change.
Chemical Change
A chemical change is a change in which one or more new substances are formed with different chemical properties due to a change in the chemical composition of the original substance.
Example:
- Rusting of iron
- Burning of wood
- Cooking of food
- Curd formation from milk
Characteristics of Chemical Change
The main characteristics of a chemical change are:
- Formation of a new substance: One or more new substances with properties different from the original substance are produced.
- Change in chemical composition: Atoms rearrange and new chemical bonds are formed, resulting in new molecules.
- Usually irreversible: Most chemical changes cannot be easily reversed to obtain the original substance.
- Energy change occurs: Chemical changes often involve the absorption or release of energy in the form of heat, light, or sound.
- Chemical reaction takes place: Bonds are broken and new bonds are formed during the process.
- Properties change completely: The new substance has different physical and chemical properties from the original substance.
- Observable changes may occur: Such as change in colour, evolution of gas, formation of a precipitate, or change in temperature.
Physical vs Chemical Change
| Physical Change | Chemical Change |
|---|---|
| A physical change is a change in which only the physical properties of a substance change. | A chemical change is a change in which a new substance is formed. |
| No new substance is produced. | New substance with different properties is produced. |
| The composition of the substance remains the same. | The composition of the substance changes. |
| Usually reversible in nature. | Usually irreversible in nature. |
Involves small energy change. | Involves significant energy change. |
No chemical reaction occurs. | A chemical reaction takes place. |
Only arrangement of particles changes. | New bonds are formed and old bonds are broken. |
| Example: melting of ice, cutting paper. | Example: rusting of iron, burning of wood. |