8th Ch 2 Phase ChangesHeat Energy

1
8th Ch 2 Phase Changes/Heat Energy

• Adapted from Matter-Building Block of the
  Universe
• Prentice-Hall
• By Jim Barnaby

2
Kinetic Theory of Matter

• Kinetic Theory
• Explanation of how particles in matter behave

3
Assumptions of Kinetic Theory

• 3 Assumptions of the kinetic theory
• All matter is composed of small particles (atoms,
  molecules, ions)
• These particles are in constant random motion
• These particles are colliding with each other and
  the walls of their container

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Matter

• Matter
• Anything with mass and volume
• Matter can exist in 4 phases (solid, liquid, gas,
  plasma)
• Phase is an important physical property of matter

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Phases of matter--Solid

• Phases (states) of Matter
•  
• SolidDefinite shape and definite volume
• A solid can break into smaller pieces, but pieces
  maintain a definite shape

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Solid

• Solid molecules vibrate about fixed positions,
  but they cannot move past one another.
• High temperature (heat energy)more vibrations
• Low temperature (heat energy)less vibrations
•  As a solid melts, the particles gain enough KE
  to slip out of ordered arrangement and flow
  around one another to form a liquid

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Liquid

• LiquidNo definite shape, definite volume
• -Takes the shape of its container
• Liquid molecules move faster than molecules in a
  solid and can flow around one another.
• Demo (Grains of rice when poured act exactly
  like water molecules)

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Gas

• GasNo definite shape, No definite volume
• -Diffuses to fill all available space (takes the
  shape and volume of its container)
• Demo with H2S morning breeze or perfume
• Draw on board flatulence and how it diffuses
• Boil water/ice water for gas laws demo

9
Diffusion

• Diffusion
• Spreading of particles throughout a given volume
  until they are uniformly distributed. (Occurs in
  solids, liquids and gases, but occurs most
  rapidly in gases)
•  
• Demo Drops of food coloring in water
• Vanilla flavoring in rubber balloonodor diffuses
  through spaces in rubber

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Gas molecular motion

• Gas particles are far apart (equi-distant) and
  overcome attractive forces between particles
• Gas particles are in constant motion moving
  greater than 416 meters/second (1500 km/hr).
• A single gas particle undergoes 10,000,000,000
  collisions each second
• Fast moving particles are separated by large
  distances.
• Sketch boxes of molecular motion on board

11
Plasma

• PlasmaHigh temperature, high-energy gas
• Cannot be contained by ordinary matter
• Examples sun
• Stories plasma in lab
• Self-sustaining plasma would burn through earth
  to center.
• Plasma is contained by forces gravity,
  electromagnetic

12
Viscosity

• Viscosity race Volunteers
•  Viscosity
• Resistance of a liquid to flow
• Low flow abilityvery viscoushigh viscosity
• High flow abilitynot viscouslow viscosity

13
Temperature/viscosity

• What is the effect of temperature on viscosity?
• Increase tempdecrease viscosityincrease flow
  ability
• Decrease tempincrease viscositydecrease flow
  ability
• Put honey in microwave for easy pouring

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Gas laws

• Boyles Law
• If a balloon is compressed particles collide
  with each other and the walls of the balloon even
  morecreating more pressure
•  If the volume of a gas decreases, the pressure
  increases
• If the volume of a gas increases, pressure
  decreases

15
Boyles Law

• Draw diagrams on board or word document
• Demo with balloons filled with air

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Charles Law

• Charles Law
• If the temperature of a gas increases, volume
  increases
• If the temperature of a gas decreases, volume
  decreases
• Demo with balloon on beaker of boiling water and
  ice water

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Heat

• Heat
• A form of energy caused by the internal motion
  of molecules in matter

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Temperature

• Temperature
• A measure of the average kinetic energy of
  molecules
• High temperaturehotfast moving molecules
• Low temperaturecoldslow moving molecules

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Heat Energy

• Which has more heat energy?
• 500 ml of 90? C water
• 50 ml of 90? C water
• Which will give the worst burn? Explain.

20
Thermometer

• Thermometer
• Instrument to measure temperature, as liquid
  mercury gets warmer it expands and rises.

21
Temperature scales

• Temperature scales
• Sketch thermometers on board
• Celsius scale based on freezing and boiling point
  of water
• Kelvin scale based on absolute zero
• Fahrenheit scale based on ?????? (absolutely
  nothing) USA is only country to use this
  scaledue to the smaller degrees (do not need to
  use decimals)

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Water Temperature chart

• Use word document to show on board
• Absolute zero
• Lowest temperature known
• Temperature at which all molecular motion stops

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Temperature conversions

• Temperature Scale Conversions
• ?C K 273
• K ?C 273
• ?C 5/9 (?F 32)
• ?F (9/5 ?C) 32
•  Do several practice conversion problems on board
  
• What temperature is the same for both Celsius and
  Fahrenheit temp scales?

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Expansion of Matter

• Expansion of matter
• Expansion joints in concrete. Objects typically
  expand as they are heated and contract as they
  cool
• Particles move faster and separate as
  temperature rises.

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Thermal Expansion

• Thermal Expansion
• Increase in size of something as temperature is
  increased.
• Participate in demos

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Water (liquid gold)

• Water
• Polar molecules H2 end and O end (draw on
  board)
• Highly positive and highly negative sides
• Water molecules orient themselves by chargewhich
  creates empty spacesthese empty spaces are
  larger in ice
• Therefore, water expands as it freezesice is
  less dense than water and floats in water

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Waterlife sustainer

• Water is one of very few substances that expands
  as it freezes
• This property of water allows life on earth
• Examples frozen lakes, freeze-thaw weathering
  of rocks

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Phase changes

• Phase changes
• Energythe only difference between water in the
  solid phase (ice) and water in the liquid phase
  is the amount of energy possessed by the
  particles of water.
• Draw heat energy continuum on board

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Matter Vs. Heat energy

• Matter can change phase when energy is added or
  taken away.
• Adding or taking away heat energy is the easiest
  way to change between phases of matter.
• Draw heat energy continuum and phase change
  drawing on board

30
Melting and MP

• Melting
• A solid absorbs heat energy and changes to a
  liquid
•  Melting Point (MP)
• Temperature at which a solid changes to a liquid
  (physical property)

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Common MPs

• Melting is a cooling process as heat energy is
  absorbed (taken) from the surrounding environment
  (ex melting ice cools items left in a cooler)
• Common melting points
• Water (ice) 0?C
• Salt (NaCl) 801?C
• Diamond (C) 3700?C

32
Freezing

• Freezing
• A liquid loses heat energy and changes to a
  solid
• Freezing is a warming process as lost heat energy
  is transferred to the surrounding environment
  (ex freezing water keeps oranges from freezing)

33
Freezing point (FP)

• Freezing Point (FP)
• Temperature at which a liquid changes to a solid
• Common freezing points
• Water (ice) 0?C
• Salt (NaCl) 801?C
• Diamond (C) 3700?C
• Anti-freeze (ethylene glycol) -37?C

34
FP Enlightenment

• Oh my gosh, the freezing point is the same as the
  melting point for a substance.
•  
• Freezing point melting point (same temp)

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Vaporization

• Vaporization
• Particles of liquid absorb heat energy and
  change to a gas
•  
• 2 types of vaporization are evaporation and
  boiling.

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Evaporation

• Evaporation
• Vaporization that occurs at the surface of a
  liquid as it changes to a gas (vaporizes at
  temperatures below the boiling point)
• Evaporation is a cooling process (swimming pool
  in early June)

37
Perspiration

• As water (perspiration) evaporates it absorbs and
  carries heat energy away from your body,
  therefore, our body is cooled off.
•  
• Which will evaporate and cool your body faster,
  water or rubbing alcohol? Why?
• Alcohollower boiling point (bp) allows it to
  evaporate faster

38
Boiling

• Boiling
• Vaporization occurs within the liquid as it
  changes to a gas (bubbles of steam rise in water
  as they are less dense than the water)
• Boiling is a cooling processthe temperature does
  not rise above 100?C until all water has boiled
  into steam.
•  Pressure of vapor in liquid equals pressure of
  vapor on surface of liquid

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Boiling point

• Boiling Point (BP)
• Temperature at which a liquid boils and changes
  to a gas
• Common boiling points
• Water (ice) 100?C
• Salt (NaCl) 1413?C
• Diamond (C) 4827?C

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Evaporation Vs. Boiling

• Know how to differentiate between boiling and
  evaporation. This will be on the quiz.
• Draw diagrams on board
• What is the effect of wind on evaporation of a
  body of water? Explain.

41
Altitudes effect on BP

• At high altitudes, air pressure is much lower
  therefore the boiling point of water is lower.
• A 3-minute egg boiled in Florida (sea level)
  would take 7 minutes on top of Longs Peak
  (14,200 feet)

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TDSs effect on BP

• Why do we add salt to boiling water?
• Because grandma told us to
• Salt actually raises the boiling pointmaking the
  water boil at a hotter temperaturecooking the
  food much faster due to higher temperature

43
Condensation

• Condensation
• A gas loses heat energy and changes to a liquid
• Condensation is a warming process as lost heat
  energy is released to the immediate surroundings
•  Ex. glasses on a cold day fog up as we walk
  inside, water droplets on outside of a cold
  glass, fog from breath on cold day, water vapor
  condenses to clouds

44
Sublimation

• Sublimation
• A solid absorbs heat energy and changes to a gas
  (or, a gas loses heat energy and changes to a
  solid)
• Ex. dry ice, clothes freeze and dry on
  clothesline, air (room) fresheners, snow
  disappears on cold day (temp below mp)

45
Anyone hungry?

• Make and enjoy fried ice. Anyone hungry?
•  As matter changes phases it changes physical
  properties but it remains the same kind of
  matter.
•  
• On board, draw and label the phase change diagram
  of water.
• Students answer related questions.

46
Properties of Matter

• Do properties of matter worksheet. Handout and
  have students work on. Use overhead and grade as
  a class.
• Which will boil at a higher temperature, tap
  water or distilled water (pure water)? Explain.
• Demo boil (microwave) eachtake temperature of
  eachgoggles and stand backuse tongs to drop a
  sugar cube in each.

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