Chapter 4 States of Matter

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Chapter 4States of Matter

• Section 4-1
• Solids

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• Quiz next class on Sec. 4-1

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How can we explain this?
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Lets do a quick review of what you already know

• Matter has three states
• Solid
• Liquid
• Gas
• Matter is anything that takes up space and has
  mass.

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More review

• Most matter is made up atoms and molecules.
• An atom is the smallest particle that makes up a
  given element of matter.

• When two or more atoms combine, they make a
  particle called a molecule.

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Examples of molecules
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???

• Why is water a liquid, nitrogen a gas and glucose
  a solid?
• What makes a solid a solid?
• a liquid a liquid?
• a gas a gas?

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• One clue to this mystery was first reported in
  1827 by scientist Robert Brown
• Brownian Motion

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Under a microscope, dust particles can be seen to
move in a random, jerky way.
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• The water molecules surrounding the dust particle
  are in constant, random motion.
• When they hit the dust particle, they push it in
  random directions

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Matter in motion

• The idea that the particles (atoms and molecules)
  of all matter are in constant, random motion is
  called the kinetic theory of matter.

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Kinetic Theory of Matter

• All matter is made of atoms and molecules.
• These particles are always in motion.
• The higher the temperature, the faster the
  particles move.

• At the same temperature, heavier particles move
  slower and lighter particles move faster.

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Temperature and Heat

• What makes hot tea different from cold iced tea?
• Same particles
• movement of particles is different
• Higher temp faster moving particles

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Temperature and Heat

• Lower the temperature and the particles slow
  down.
• At very low temperatures the motion of the
  molecules is very slow.
• You cannot make things so cold that the motion
  completely stops,

but . . .
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• scientists have come close.

The temperature at which the particles of matter
would completely stop is called
absolute zero.
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Absolute zero is - 273.15 C
You cant get colder than that, no matter how
hard you try
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Transfer of heat

• When hot matter touches colder matter, faster
  moving particles collide with slower moving
  particles.
• The faster moving particles give some of their
  energy to the slower moving particles.

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Matter in the solid state

• In a solid, the particles vibrate or shake back
  and forth
• but do not move from their position in respect to
  each other.

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The particles vibrate about a fixed position.
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Crystals or Crystalline Solids

• Particles of crystals are arranged in repeating
  geometric patterns

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• Table salt crystals are shaped like cubes.

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• Diamond, a form of carbon, is also a crystalline
  solid.
• the crystals are shaped something like pyramids.

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Non-crystalline solids

• Many solids do not form crystals.
• Their molecules do not arrange into repeating
  patterns
• often because they are too large.
• Examples
• glass
• many plastics

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How does a solid become a liquid?

• Start with very cold ice and gradually heat it.
• If you could see the molecules, you would
  see each molecule shaking faster and faster,

but still held in one position by the other
molecules around it.
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Keep heating your ice

• When the temperature reaches 0 C, the molecules
  begin to break free.
• The molecules begin to move freely around each
  other.
• The molecules enter the liquid state.

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• Melting point
• the temperature at which a substance
  changes from a solid to a liquid.

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Temperature (C)
60
20
0
-20
0
Heat (kilojoules)
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Temperature (C)
60
20
0
-20
0
Heat (kilojoules)
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• The amount of heat required to melt 1 kg of a
  solid is called its

heat of fusion
measured in kilojoules per kilogram k J / k g
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Temperature (C)
0
Heat (kilojoules)
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• Waters heat of fusion is
• 334 kJ/kg
• That is the same amount of energy you would spend
  if you climbed all the stairs in a 110-story tall
  building.

No, not a 110-foot tall building . . .
a 110-story building!
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Freezing

• As you know, if you can melt something, you can
  cool the liquid again to freeze it.
• When you cool a liquid, the particles begin to
  slow down.
• The attractive forces between the particles begin
  to catch the particles,
• and crystals begin to form.

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• Freezing point
• the temperature at which attractive forces trap
  particles in a cooling liquid and form crystals.

Think If the melting point of iron is 1,535 C,
at what temperature does iron freeze?
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Non-crystalline solids

• Non-crystalline solids, like glass, butter or
  wax, do not have a definite freezing or melting
  point.

• If you slowly heat cold butter, it gradually
  gets softer and softer until it is completely
  liquid.

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