Unit 8, Chapter 25

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Unit 8, Chapter 25
CPO Science Foundations of Physics
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Unit 8 Matter and Energy
Chapter 25 Energy, Matter, and Atoms

• 25.1 Matter and Atoms
• 25.2 Temperature and the Phases of
  Matter
• 25.3 Heat and Thermal Energy

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Chapter 25 Objectives

• Describe the relationship between atoms and
  matter.
• Find an element in the periodic table.
• Identify the differences between elements,
  compounds, and mixtures.
• Convert temperatures between Fahrenheit, Celsius,
  and Kelvin scales.
• Understand the concept of absolute zero
  temperature.
• Describe the phases of matter and explain solid,
  liquid, and gas in terms of energy and atoms.
• Describe the concepts of heat and thermal energy
  and apply them to real-life systems.
• Perform basic calculations with specific heat.

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Chapter 25 Vocabulary Terms

• atom
• compound
• element
• mixture
• molecule
• periodic table
• Kelvin
• Celsius
• thermometer
• Fahrenheit

• specific heat
• temperature
• calorie
• absolute zero
• random
• melting point
• heat of vaporization
• boiling point
• evaporation
• ionized

• condensation
• thermal energy
• relative humidity
• British thermal unit (BTU)
• heat
• solid
• plasma
• liquid
• heat of fusion
• gas

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25.1 Matter and Atoms

• Key Question
• What are the properties of different elements?

Students read Section 25.1 AFTER Investigation
25.1
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25.1 Matter and Atoms

• We have partial answers to these three questions
  for all types of matter
• What is the smallest piece of matter?
• Why can the same kind of matter assume different
  forms, like solid or liquid?
• How can one kind of matter (like wood) turn into
  another kind of matter with very different
  properties (like ashes)?

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25.1 Brownian Motion

• A large floating dust speck moves smoothly
  because it is much larger than a particle of
  water.
• A tiny dust speck shows Brownian motion because
  of collisions with particles of water.

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25.1 Size of atoms

• The head of a pin contains more than 1020 atoms.
• A sheet of thin aluminum foil is 200,000 atoms
  thick.

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25.1 Classification of matter

• A molecule is a group of two or more atoms that
  are joined together.
• Most matter you encounter is made of molecules,
  or mixtures of molecules.

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25.1 First theory of matter

• The ancient Greeks proposed that all matter was
  made of four fundamental elements
• air, fire, water, and earth.

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25.1 Elements

• Today we know that nearly all the matter in the
  world is made from 92 different elements.
• The periodic table shows the elements in order
  from atomic number 1 (hydrogen) to number 92
  (uranium).

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25.1 Elements

• At the time of this writing, scientists have
  created elements 93 to 116 in research
  laboratories.

• We dont find much of elements 93 to 116 in
  nature because all of these elements are
  radioactive and break down into other elements.

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25.2 Temperature and the Phases of Matter

• Key Question
• What is temperature?

Students read Section 25.2 AFTER Investigation
25.2
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25.2 Temperature and the Phases of Matter

• In the Fahrenheit scale, water freezes at 32
  degrees and boils at 212 degrees
• The Celsius scale divides the difference between
  the freezing and boiling points of water into 100
  degrees (instead of 180).

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25.2 Converting temperatures

• A friend in Paris sends you a recipe for a cake.

• The French recipe says to bake the cake at a
  temperature of 200C for 45 minutes.
• At what temperature should you set your oven,
  which reads temperature in Fahrenheit?

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25.2 Temperature and the Phases of Matter

• All thermometers are based on some physical
  property (such as color or volume) that changes
  with temperature.
• A thermistor is a device that changes its
  electrical resistance as the temperature changes.
• A thermocouple is another electrical sensor that
  measures temperature.

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25.2 Temperature and the Phases of Matter

• Temperature measures the kinetic energy per atom
  due to random motion.
• Random motion is motion that is scattered equally
  in all directions.
• In pure random motion the average change in
  position is zero.

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25.2 Temperature and the Phases of Matter

• When the temperature gets down to absolute zero,
  the atoms are said have the lowest energy they
  can have and the temperature cannot get any
  lower.
• Technically, we believe atoms never stop moving
  completely.
• Figuring out what happens when atoms are cooled
  to absolute zero is an area of active research.

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25.2 Temperature and the Phases of Matter

• The Kelvin temperature scale is useful for many
  scientific calculations because it starts at
  absolute zero.
• The Kelvin scale is used because it measures the
  actual energy of atoms.
• A temperature in Celsius measures only the
  relative energy, relative to zero Celsius.

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25.2 Phases of Matter

• The three most common phases of matter are called
  solid, liquid, and gas.
• At temperatures greater than 10,000 K the atoms
  in a gas start to break apart.
• In the plasma state, matter becomes ionized.

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25.2 Phase changes

• When thermal energy is added or subtracted from a
  material, either the temperature changes, or the
  phase changes, but usually not both at the same
  time.

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25.2 Change from solid to liquid

• The melting point is the temperature at which a
  material changes phase from solid to liquid.
• Melting occurs when the kinetic energy of
  individual atoms equals the attractive force
  between atoms.
• The heat of fusion is the amount of energy it
  takes to change one kilogram of material from
  solid to liquid or vice versa.

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25.2 Energy and Heat of Fusion
Heat of Fusion (J/kg)
E mhf
Heat energy (J)
Mass (kg)
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25.2 Calculate Energy

• How many joules does it take to melt a 30 gram
  ice cube at 0C?

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25.2 Evaporation

• Evaporation occurs when molecules go from liquid
  to gas at temperatures below the boiling point.
• Evaporation takes energy away from a liquid.
• The average energy of the molecules left behind
  is lowered.
• Evaporation cools the surface of a liquid because
  the fastest molecules escape and carry energy
  away.

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25.2 Condensation

• Condensation occurs when molecules go from gas to
  liquid at temperatures below the boiling point.
• Condensation raises the temperature of a gas
  because atoms in a gas have more energy than
  atoms in a liquid.
• When air is saturated, it means the processes of
  evaporation and condensation are exactly balanced.

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25.2 Change from liquid to gas

• The boiling point is the temperature at which the
  phase changes from liquid to gas.
• Just as with melting, it takes energy for an atom
  to go from liquid to gas.
• The heat of vaporization is the amount of energy
  it takes to convert one kilogram of liquid to one
  kilogram of gas.

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25.2 Energy and Heat ofVaporization
Heat of Vaporization (J/kg)
E mhv
Heat energy (J)
Mass (kg)
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25.2 Calculate Energy

• A steam iron is used to remove the wrinkles from
  clothes.
• The iron boils water in a small chamber and vents
  steam out the bottom.
• How much energy does it require to change
  one-half gram (0.0005 kg, or about half a
  teaspoon) of water into steam?

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25.3 Heat and Thermal Energy

• Key Question
• What is the relationship between heat,
  temperature, and energy?

Students read Section 25.3 AFTER Investigation
25.3
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25.3 Heat and Thermal Energy

• Temperature is NOT the same as thermal energy.
• Thermal energy is energy stored in materials
  because of differences in temperature.
• The thermal energy of an object is the total
  amount of random kinetic energy for all the atoms
  in the object.
• Remember, temperature measures the random kinetic
  energy of each atom.

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25.3 Heat and Thermal Energy

• Imagine heating a cup of coffee to a temperature
  of 100C.
• Next think about heating up 1,000 cups of coffee
  to 100C.
• The final temperature is the same in both cases
  but the amount of energy needed is very different.

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25.3 Heat and Thermal Energy

• Heat is what we call thermal energy that is
  moving.
• The joule (J) is the unit of heat (or thermal
  energy) used for physics and engineering.
• The calorie is a unit of heat often used in
  chemistry.

Heat flows from the hot coffee to the cooler air
in the room.
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25.3 Specific Heat

• The specific heat is the quantity of heat it
  takes to raise the temperature of one kilogram of
  material by one degree Celsius.

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25.3 Specific Heat

• The temperature of gold rises quickly compared
  with water because its specific heat is much less
  than the specific heat of water.

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25.2 Heat Equation
Specific heat (J/kgoC)
Heat energy (J)
E mcp(T2-T1)
Change in Temperature (oC)
Mass (kg)
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25.2 Calculate Heat

• One kilogram of water is heated in a microwave
  oven that delivers 500 watts of heat to the
  water.
• One watt is a flow of energy of one joule per
  second.
• If the water starts at 10C, how much time does
  it take to heat up to 100C?

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26.3 First Law of Thermodynamics

• Energy loss is equal to energy gain.

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26.3 Second Law of Thermodynamics
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Application The Refrigerator