Physical Changes:
* No new substances are formed. The molecules themselves remain the same, but their arrangement or state of matter might change.
* Often reversible. The original substance can be recovered through simple means.
* Usually involve changes in physical properties like shape, size, color, state of matter (solid, liquid, gas), density, etc.
Examples:
* Melting ice: Water changes from solid to liquid, but its chemical composition (H₂O) remains the same.
* Boiling water: Water changes from liquid to gas, but it's still water.
* Cutting paper: The paper changes shape, but its chemical makeup stays the same.
* Dissolving sugar in water: The sugar disappears, but it's still present in the water as dissolved sugar molecules.
Chemical Changes:
* New substances are formed. The atoms are rearranged to form new molecules with different properties.
* Usually irreversible. The original substances cannot be easily recovered.
* Often involve changes in chemical properties like flammability, reactivity, and acidity.
Examples:
* Burning wood: Wood reacts with oxygen to produce ash, carbon dioxide, and water - entirely different substances.
* Rusting iron: Iron reacts with oxygen and water to form iron oxide (rust), a different substance.
* Baking a cake: The ingredients react with each other to form a cake, a new substance with different properties.
* Digesting food: The food is broken down into simpler molecules, creating entirely different substances.
Here's a simple way to remember the difference:
* Physical Changes: You can usually reverse the change and get back the original substance. Think of it as changing the appearance but not the fundamental makeup.
* Chemical Changes: You usually can't reverse the change easily. Think of it as creating something entirely new with different properties.
