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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

Physical vs. Chemical

Properties and Change

physical properties
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
Physical Changes
  • Changes in which no new substance is formed
    • Changes of state
      • Melting
      • Boiling
      • Freezing
      • Condensation
      • Sublimation
    • Sharpening a pencil
physical changes cont
Physical Changes (cont)
  • Taking a bite of food
  • Slicing an onion
  • Breaking of glass
  • Etc.
evaporation
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
boiling
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?
boiling cont
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?
chemical properties
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
chemical change
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
uses of chemical and physical properties
Uses of Chemical and Physical Properties
  • To separate substances
  • To identify substances
  • To distinguish between substances
  • To predict usefulness of new substances
melting vs dissolving
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
h4 c2
H4 – C2
  • 2 - 5, 8, 12, 14, 36, 39 - 41, 54, 61
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