Phases and Phase Changes

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Phases and Phase Changes
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What is a phase?

• Matter can exist in certain states, or phases
• Each phase tells us how much energy the matter
  contains
• The 4 most common phases are solids, liquids,
  gases, and plasma

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Solids Matter at its most Content

• A piece of matter in its solid form is very
  relaxed, not moving around very much.
• This helps explain a solids definite shape and
  volume
• Solids are very much like old folks sitting in a
  rocking chair

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Solids and Order

• Besides being very relaxed, solids are also very
  ordered and predictable
• http//www.edinformatics.com/interactive_molecules
  /ice.htm

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Liquids Slightly More Risqué

• While solids are very relaxed, liquids are a
  little more energetic
• They are somewhat like young-adults plenty of
  energy, but they arent totally out of control

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Liquids, Part 2

• Liquids are somewhat stuck together, so they have
  a definite volume
• The attraction isnt very strong, so liquids can
  flow somewhat, giving them an indefinite shape
• Its sort of like a crowd of people that all move
  together

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Gases Total Chaos

• Gases have even more energy than liquids
• Gas particles are constantly moving through
  space, going in every direction
• This constant motion helps explain their
  indefinite volume and shape

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Plasma Beyond Chaos

• Believe it or not, it is possible for matter to
  have more energy in another phase, called plasma
• A plasma is a high-temperature gas with an
  electric charge (/-)
• If gases are like kindergartners, plasmas are
  like ADHD kindergartners hopped up on sugar

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Where is plasma?

• Plasma isnt common on Earth, although we do have
  it (TVs, lights)
• Plasma is mostly found in stars, which makes it
  the most common form of matter in the universe
  (around 95)

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• http//web.visionlearning.com/custom/chemistry/ani
  mations/CHE1.1-an-threestates.shtml

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Always a solid, liquid or gas?

• We have seen examples where matter is not
  necessarily one phase

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Phase Changes

• Anytime matter transitions from one phase to
  another, we say that it has gone through a phase
  change
• As different phases have different amounts of
  energy, every phase change also involves an
  energy change

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Endo or Exo?

• Phase changes that involve a release of energy
  are called exothermic
• Phase changes that absorb energy are called
  endothermic
• Examples melting is endothermic, condensation
  is exothermic

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of Phase Changes

• There are 6 possible phase changes, 2 between
  each phase
• Between solids and liquids are melting and
  freezing
• Between liquids and gases are condensation and
  vaporization
• Between solids and gases are sublimation and
  deposition

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Solids and Liquids

• Melting is an endothermic process were all
  familiar with
• Freezing is an exothermic process, as solids have
  less energy than liquids

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Gases to Liquids Condensation

• Condensation is a process we all know about (coke
  can on a hot summer day, morning dew)
• Condensation is an exothermic process, as you
  know if youve ever had a steam burn
• The formula for condensation is this
• Hot, humid air cold surface ? condensation

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Examples

• http//www.carteretcountyschools.org/chs/fptwebs/J
  MILBOURNE/Physics/video20clips/mach1.mpg
• The Michigan State-UVA game

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Vaporization Going Gaseous

• Vaporization is an endothermic process involving
  a gas turning into a liquid
• There are two types of vaporization evaporation
  and boiling

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Evaporation

• Evaporation involves liquid particles at the
  surface getting hit from below by other liquid
  particles from below

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• Its like one of those turbo-mega-jackpot
  ping-pong ball lottery devices

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• The liquid particles at the surface gain energy
  from the collisions, enough to be considered a
  gas
• Once energized, they can float off into the
  surrounding air
• The remaining liquid has less energy

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Boiling

• Evaporation must take place at a liquids surface,
  but boiling can take place anywhere
• The liquid?gas change occurs within the liquid,
  forming small bubbles that float to the surface

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Pressure, Under Pressure

• The ease with which these bubbles forms depends
  on the air pressure at the liquids surface
• The more pressure, the harder it is to form the
  bubbles the less pressure, the easier
• Water boils at lower temperatures at higher
  altitudes

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Solids and Gases

• While not very common, phase changes between
  solids and gases do occur
• Sublimation is a phase change from solid to gas
  (dry ice)

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• http//www.dac.neu.edu/physics/b.maheswaran/phy112
  1/data/ch04/anim/anim0406.htm

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• Deposition involves a gas changing phases back
  into a solid

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Which Sets of Phase Changes are Similar and Why?

• Melting and freezing
• Condensation and deposition
• Freezing and evaporation
• Sublimation and condensation

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How Much Does it Cost?

• Changing phases involves an energy change, but
  how much?
• We can tell this by looking at a heating curve
• http//www.dac.neu.edu/physics/b.maheswaran/phy112
  1/data/ch04/anim/anim0405.htm

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• The energy necessary to change matter from a
  solid to a liquid is called the heat of fusion
• The energy necessary to change matter from a
  liquid to a gas is called the heat of vaporization

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