Physical vs. Chemical Changes

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Physical vs. Chemical Changes
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Goal How do you tell the difference between
chemical and physical changes?
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• Physical Change
• A change in any objects physical properties
• any change in an objects
• - mass - color
• - weight - shape
• - volume - hardness
• - density - texture

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Physical Changes

• Changes in Density, Mass or Volume D M/V

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Physical Changes

• Creating mixtures that can be separated out -
  mixtures can be reversed.

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Physical Changes

• Changes in Phase of Matter

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Example of a Physical Change
A Melting Icicle
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• physical properties characteristics of a
  substance that can be observed without changing
  the identity of the substance.
• ex.) wood is still wood whether it is shaped
  into a baseball bat or used to build the walls of
  your house or if its still in the shape of a
  tree!
• ex.) water is still water whether it is in the
  form of ice, liquid water, or water vapor. Its
  still H2O!

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Review Other Physical Properties

• Color
• Size
• Shape
• Texture
• Magnetism

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Chemical Changes

• Chemical Changes occur when atoms react with
  other atoms to form chemical bonds.
• When atoms are bonded together they make a
  molecule.

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Chemical Changes

• When a chemical reaction happens the new
  molecules are a new substance or compound.
• A B ? AB

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• Chemical Change
• gt changes that substances undergo when they turn
  into other substances
• gt Also called a Chemical Reaction
• ex.) as coal burns, O2 (in the air) combines
  chemically with C (the substance that makes up
  most of the coal) and forms a completely new
  substance CO2
• - C and O2 have changed chemically! They
• no longer exist in their original
  forms!
• - Written out C O2 CO2

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Evidence of Chemical Changes, Reactions or Bonding

• Energy being taken in or given off (heat,
  coolness, light)

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Evidence of Chemical Changes, Reactions or Bonding

• Gas or Bubbles

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Evidence of Chemical Changes, Reactions or Bonding

• Color or Texture Change

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Evidence of Chemical Changes, Reactions or Bonding

• Color and Texture Change that is not easily
  reversed

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Evidence of Chemical Changes, Reactions or Bonding

• Forming of a Precipitate (adding to solutions and
  a solid is formed)

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How to decide type of change

• Ask yourself Can I easily turn substance back to
  the way it was?
• If yes physical change
• If no chemical change
• Was the change awesome to watch?
• If yes Probably chemical change
• If no Probably physical change
• Did the name of the new substance change?
• If yes Probably chemical
• If no Probably physical

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Examples of Chemical Change

• The rusting of iron
• The baking of bread
• Burning of a match
• Fireworks

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Example of a Chemical Change The Electrolysis
of Water (H2O)
The Chemical Identity of Water ( H2O ) is changed
into the elements Hydrogen ( H2 ) and Oxygen ( O2
)