Physical Changes:
* Definition: Alter the form or appearance of a substance but don't change its chemical composition.
* Key Features:
* Usually reversible.
* No new substances are formed.
* Involve changes in physical properties like shape, size, or state of matter.
* Examples:
* Melting ice (solid to liquid)
* Cutting paper
* Boiling water (liquid to gas)
* Dissolving sugar in water
* Crushing a rock
Chemical Changes:
* Definition: Involve the formation of new substances with different chemical properties.
* Key Features:
* Often irreversible (though some are reversible).
* New substances with different properties are formed.
* Often accompanied by changes in energy, such as the release of heat (exothermic) or the absorption of heat (endothermic).
* Examples:
* Burning wood (producing ash, smoke, and gases)
* Rusting of iron (iron reacts with oxygen)
* Baking a cake (ingredients chemically change into a new substance)
* Souring milk (bacteria convert lactose into lactic acid)
* Digesting food
Here's a helpful table to summarize:
| Feature | Physical Change | Chemical Change |
| -------------- | --------------- | --------------- |
| Composition | Remains the same | Changes |
| Reversibility | Usually reversible | Often irreversible |
| New substances | No | Yes |
| Examples | Melting, freezing, boiling, cutting, dissolving | Burning, rusting, cooking, digestion |
In essence, a physical change affects the form of a substance while a chemical change alters its chemical makeup.
