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Physical vs. Chemical

Physical vs. Chemical. Properties and Change. Physical Properties. Properties that can be observed or specified without changing substance into another. Color Odor Taste Size Density Physical State BP and MP. Physical Changes. Changes in which no new substance is formed

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Physical vs. Chemical

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  1. Physical vs. Chemical Properties and Change

  2. Physical Properties • Properties that can be observed or specified without changing substance into another. • Color • Odor • Taste • Size • Density • Physical State • BP and MP

  3. Physical Changes • Changes in which no new substance is formed • Changes of state • Melting • Boiling • Freezing • Condensation • Sublimation • Sharpening a pencil

  4. Physical Changes (cont) • Taking a bite of food • Slicing an onion • Breaking of glass • Etc.

  5. Evaporation • Some molecules have enough energy to escape the surface • Opposite of condensation • In equilibrium in closed system • In open system will eventually all evaporate because of diffusion in air. • Makes smells possible • No odor without evaporation • Molecules must be at least slightly soluble in water

  6. Boiling • As temperature of liquid increases: • Vapor pressure of liquid increases • (more molecules have enough energy to escape) • So liquid evaporates faster • When vapor pressure reaches atmospheric pressure: • Liquid boils (bubbles form in the liquid and escape) • Boiling is a cooling process. How?

  7. Boiling (cont) • Why is boiling point constant? • So you don’t cook things faster by boiling faster. • Only constant at constant atmospheric pressure. • For same reason, melting point is constant • mp doesn’t depend on pressure, why? • Why is boiling with a microwave strange?

  8. Chemical Properties • Properties exhibited under changes in composition • They describe how a substance can change into other substances • Iron rusts • Baking soda decomposes with heat • Flammability or non-flammability • Wax burns, water doesn’t

  9. Chemical Change • A change in which a new substance or substances are formed. • Also called a chemical reaction • Rusting of iron • Digesting food • Burning gasoline or anything • Detonating dynamite • Souring of milk

  10. Uses of Chemical and Physical Properties • To separate substances • To identify substances • To distinguish between substances • To predict usefulness of new substances

  11. Melting vs. Dissolving • Melting is a change of state involving heat but not a solvent. • Dissolving is a physical change also, but involves a solvent and not necessarily heat

  12. H4 – C2 • 2 - 5, 8, 12, 14, 36, 39 - 41, 54, 61

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