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AP Chemistry Unit 4.4 Physical and Chemical Changes

Physical vs Chemical Changes

  • A physical change is a change in the form of a substance, not in its chemical composition = reversible
    • A physical change can be used to separate a mixture into pure compounds, but will not break compounds into elements
      • Ex: phase changes, separation techniques (Distillation, filtration, chromatography), dissolving
    • Involve changes in intermolecular forces
    • Physical properties: shape, solubility, density, volume, & interparticle distance at diff temperatures (& phases) may change but composition stays the same
  • Chemical change: a substance becomes a new substance with different properties and composition
    • Ex: rusting, bunsen burner (burning), acid, combustion (reacted with oxygen)
    • In chemical changes, one substance changes to another by reorganizing the way the atoms are attached to each other → involve changes in intramolecular forces
      • Bonds have been broken, and new ones have been formed
    • Indicators of chem change: temp, light, or color change, gas or precipitate formation

Example: Dissolving NaCl

  • Can be argued both ways bcuz is reversible (physical change) and ionic bonds are broken (chemical)
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