Chemical vs. Physical Change
Chemical changes result in new substances with different properties, while physical changes alter appearance but not chemical composition.
Core Principles
- Chemical changes involve breaking and forming chemical bonds, creating entirely new substances (e.g., burning wood).
- Physical changes alter the form or appearance of a substance without changing its chemical identity (e.g., melting ice).
Key Terms
- Chemical Change: A process that involves the rearrangement of the structure of molecules or compounds, resulting in the formation of new substances with different properties.
- Physical Change: A change in the form or appearance of a substance that does not alter its chemical composition.
Real World Examples
- Burning wood: This is a chemical change because the wood reacts with oxygen to produce ash, carbon dioxide, and water vapor, all new substances.
- Melting ice: This is a physical change because the solid water (ice) turns into liquid water, but it remains H₂O.
- Rusting of iron: A chemical change where iron reacts with oxygen and water to form iron oxide (rust), a new compound.
- Boiling water: A physical change where liquid water turns into steam (gaseous water), but it is still H₂O.
- Dissolving sugar in water: A physical change because the sugar molecules disperse in the water, but they can be recovered by evaporating the water.
- Baking a cake: A chemical change involving reactions between ingredients that create new compounds, altering taste, texture, and appearance.
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