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Understanding Changes in Matter

Learn about physical and chemical changes, including phase changes and evidence of chemical change. Explore conservation of mass and examples of chemical reactions.

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Understanding Changes in Matter

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  1. Changes in Matter

  2. Physical Change • The form or appearance of the sample may change but the identity remains the same. • Crumpling • Cutting, crushing, grinding,tearing • Phase changes • Dissolving

  3. Representing Change • Use “equations” to show change. Substances Before  Substances After By the Way In a physical change, you have the same stuff before & after. The formulas match!

  4. Dissolving • Dissolving is a physical change. • Think of sugar in water. You still have sugar – you just spread it out and put water molecules in between. • C6H12O6(s)  C6H12O6(aq) =

  5. Dissolving source

  6. Phase Changes • Phase changes are physical changes. • No new substance is created (chemical formula stays the same) • ice melting: H2O(s)  H2O(l) • water boiling: H2O (l)  H2O(g)

  7. Chemical Change • In a chemical change the identity of the matter is changed. • A new substance with unique properties is formed. • The chemical formula changes. • Ex: 2H2O(l)  2H2(g) + O2(g) 

  8. Chemical decomposition of water. 2H2O(l)  2H2(g) + O2(g) Decomposition = Reaction where a molecule breaks down into simpler substances. source

  9. 2H2O(l)  2H2(g) + O2(g)

  10. Burning • Common name for an oxidation reaction. • Burning means reacting with oxygen. • Burning is a chemical change, because the original substance is changed into new kinds of matter. • Ex: CH4(g) + 2O2(g)  CO2(g) + 2H2O(g) Formulas don’t match!

  11. CH4(g) + 2O2(g)  CO2(g) + 2H2O(g) Formulas don’t match! source

  12. Other Chemical Changes • Cooking • Fermentation • Corrosion • Rotting • Explosion • Synthesis

  13. Evidence of Chemical Change • Produce Heat • Produce Light • Evolution of a Gas • Formation of a Precipitate • Change in Properties …meaning… Create something NEW

  14. Conservation of Mass • Mass is neither created nor destroyed. • Mass is conserved. • Massreactants = Massproducts • Massbefore = Massafter • # of atoms before = # of atoms after

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