Phases of Matter

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Phases of Matter

• Overview
• Solid, liquid, gas (vapor) properties
• Molecular motion vs. phase
• Gases and pressure
• Liquids, evaporation, boiling
• Solids, melting

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Properties of the different phases

• 1-1. In your group, list the different physical
  properties of
• Solids
• Liquids
• Gases or vapors

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Solids

• Fixed volume and shape
• Heating ? melting
• Powders vs. chunk of something
• Crystals

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Liquids

• Fixed volume, but adopt shape of container
• Wet, pourable
• Heating ? vaporization (boiling)
• Cooling ? freezing

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Gases or Vapors

• No fixed volume or shape, assume shape and volume
  of container
• Cooling ? condensation

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What is the difference at the molecular level?

• Molecules are always in motion kinetic energy
• Molecules are attracted to each other
  (intermolecular forces)
• Amount of motion related to substance and
  temperature
• Solid
• Atoms/molecules very close to each other in
  crystal lattice
• Fixed positions relative to each other
• Molecular motion vibrational only

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Crystal LatticeNaCl
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Crystal Lattice
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Crystal lattice of molecular solid
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Water crystal lattice
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Energy and Molecules

• Energy and phases of matter
• Molecules are always in motion kinetic energy
• Amount of motion related to temperature

Solid crystal lattice, molecular motion is
predominantly vibrational
Liquid molecules in close proximity, molecular
motion is vibrational, rotational, translational
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Liquids

• Rotational motion molecules can rotate in space
  (spinning)

Translational motion molecules move relative to
each other
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Liquids

• Molecules are close together (attractive forces)
  but have a lot of freedom of movement. Gives
  rise to macroscopic properties associated with
  liquids
• Can pour a liquid,
• Adopts shape of container
• Viscosity resistance to flow

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Energy and Molecules

• Energy and phases of matter
• Molecules are always in motion kinetic energy
• Amount of motion related to temperature

Solid crystal lattice, molecular motion is
predominantly vibrational
Liquid molecules in close proximity, molecular
motion is vibrational, rotational, translational
Gas molecules widely separated, translational
motion predominates
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Gas or Vapor Phase

• Molecules are far apart no intermolecular forces
• Molecules move independently of each other, shape
  and volume of container
• Translational motion predominates
• Elastic collisions w/ other gas molecules and
  with container walls
• Collisions with container walls gives rise to
  pressure

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Phase Changes

• Molecular motion (Kinetic Energy, KE) increases
  with temperature
• KE ? Tabs (Kelvin scale)
• KE ½ mv2
• m mass, v velocity
• (Kinetic Molecular Theory)

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Phase Changes Solid ? Liquid

• Solid vibrational motion increases with
  temperature until energy overcomes intermolecular
  forces to some extent.
• Lattice collapses but molecules still in close
  proximity.
• More molecular motion possible (rotational,
  translational)
• Liquid ensues
• MELTING

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Phase Changes Liquid ? Gas

• Liquid motion (vibrational, rotational,
  translational) increases with temperature.
• Molecules eventually have enough kinetic energy
  to completely overcome intermolecular forces.
• Molecule escape into gas phase.
• VAPORIZATION

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Phase Changes Gas ? Liquid

• Vapor motion (translational) decreases with
  decreasing temperature.
• Molecules eventually do not have enough kinetic
  energy to overcome intermolecular forces stick
  together on collisions.
• Molecules cluster and form droplets of liquid.
• CONDENSATION (precipitation)

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Phase Changes Liquid ? Solid

• Liquid motion (vibrational, rotational,
  translational) decreases with decreasing
  temperature.
• Molecules stick together more and more as
  substance is cooled. Eventually form small
  crystal lattices (seed crystals, nucleation)
  which grow.
• FREEZING

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Other Phase Changes

• Solid ? Vapor sublimation (low temperature, low
  pressure)
• dry ice, frozen CO2
• snow disappearing below freezing temps
• Vapor ? Solid deposition (low temperature, low
  pressure)
• frost

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Phase Changes
gas
condensation
vaporization
deposition
sublimation
Energy of system
liquid
freezing
melting
solid
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Heating Curve
100
Temperature, ºC
75
50
25
0
25
Heat added (kJ)
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Properties of Gases (Gas Laws)

• Pressure and Temperature are directly
  proportional
• Pressure and volume are inversely proportional
• Volume and temperature are directly proportional
  (video)
• Volume and amount of a gas are directly
  proportional
• What is happening at the molecular level?

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Pressure (P) and Temperature (T)

• Pressure results from collisions of molecules w/
  container walls.
• As temperature (T) ?, molecules move faster (more
  KE), more collisions, P ?

T ? then P ? T ? then P ?
Directly proportional
Assumes constant volume
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Pressure (P) and Volume (V)

• Pressure results from collisions of molecules w/
  container walls.
• As Volume (V) ?, number of collisions decreases,
  P ?

V ? then P ? V ? then P ?
Inversely proportional
Assumes constant temperature
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Volume (V) and Temperature (T)

• As T increases, molecules move faster.
• To maintain same pressure, number of collisions
  must remain the same, thus V increases

T ? then V ? T ? then V ?
Directly proportional
Assumes constant pressure
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Volume (V) and Number of molecules

• Two samples of gas at the same P, T, and V
• same number of collisions
• same number of molecules

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Properties of Gases

• Explain each of the following
• Balloons hung outside in the sunshine pop.
• A hot air balloon rises up in the air.
• Collapsing can.
• Balloon in liquid nitrogen (video).
• Your water bottle shrinks when you fly to Dallas.
• How you pull liquid up in a straw.
• How a siphon works.

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Gas LawsQuantitative

• Pressure and Temperature are directly
  proportional P C1 x T
• Pressure and volume are inversely proportional

• Volume and Temperature are directly proportional
  V C3 x T
• Volume and amount are directly proportional V
  C4 x n

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Gas LawsQuantitative
V C3 x T V C4 x n

• P C1 x T

P x V n x R x T
Ideal Gas Equation (Law)
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Molecular Effusion and Diffusion

• Effusion

ACTIVITY smelly balloons
Diffusion
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Molecular Effusion and Diffusion

• Effusion

Diffusion
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Molecular Effusion and Diffusion

• Effusion

Diffusion
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Molecular Effusion and Diffusion

• Effusion

Diffusion
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Molecular Effusion and Diffusion

• Effusion Diffusion are dependent upon
• Temperature (hotter faster)
• Molecular Size (bigger slower)

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Properties of Liquids

• Intermolecular attractive forces (IMAF)
• Forces between molecules
• Like dissolves like. ? similar IMAF
• Stronger forces
• Larger molecules
• Polar molecules (like water)

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Properties of Liquids

• Viscosity resistance to flow
• As IMAF ? viscosity ?
• Viscosity ? as T ?
• Surface Tension
• Surface effect of stronger IMAF
• As IMAF ? surface tension ?
• Surface tension ? as T ?
• Surfactants

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Vapor Pressure

• Vapor pressure the pressure exerted by the vapor
  above a liquid when the liquid and the vapor are
  in dynamic equilibrium
• VERY difficult conceptually for students

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Vapor Pressure
Pvap
Dynamic equilibrium molecules ? vapor
molecules ? liquid
Molecules escape into vapor phase
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Vapor Pressure

• Pvap ? as T ?
• When Pvap Patm boiling
• Bubbles of gas in liquid

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Explain the following

• How a pressure cooker works.
• Why it takes longer to cook rice or pasta at high
  altitude.
• How we were able to boil water with ice.

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Heating Curve
100
Temperature, ºC
75
50
25
0
25
Heat added (kJ)
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Phase Diagrams
solid
Critical point
liquid
Pressure
gas
Triple point
Temperature
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Phase Diagrams
solid
liquid
1 atm
Pressure
gas
Temperature
Normal melting point
Normal boiling point
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Phase Diagrams
solid
liquid
Pressure
CO2
1 atm
gas
Temperature
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Phase Diagrams
H2O
solid
liquid
1 atm
gas
Pressure
Temperature