Physical Changes:
* Definition: Alterations to a substance's appearance or form, but not its chemical composition.
* Key Characteristics:
* Reversible: Often can be reversed by changing conditions (e.g., melting ice back into water).
* No new substances formed: The molecules stay the same, just arranged differently.
* Usually involve changes in state (solid, liquid, gas) or physical properties (shape, size, color).
* Examples:
* Cutting paper
* Melting butter
* Dissolving sugar in water (sugar still exists, just dispersed)
* Boiling water (still H₂O)
* Freezing water
Chemical Changes:
* Definition: Changes that alter the chemical makeup of a substance, resulting in the formation of new substances.
* Key Characteristics:
* Usually irreversible (though some can be reversed under specific conditions).
* New substances with different properties are formed: The chemical bonds holding atoms together are broken and reformed.
* Often accompanied by signs like:
* Heat or light production/absorption (exothermic/endothermic reactions)
* Gas production (bubbles)
* Color change
* Odor change
* Formation of a precipitate (solid settling out of a solution)
* Examples:
* Burning wood (forms ash, carbon dioxide, etc.)
* Rusting metal (iron reacts with oxygen to form iron oxide)
* Baking a cake (ingredients react to form a new, edible product)
* Digesting food (breaking down complex molecules into simpler ones)
* Photosynthesis (plants use sunlight to convert carbon dioxide and water into sugar and oxygen)
Remember:
* Physical changes are about rearranging matter without changing its fundamental makeup.
* Chemical changes involve the creation of entirely new substances with different properties.
