Temperature and Heat

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Temperature and Heat
2
Watch It Spread

• Overview
• For this introductory activity you will observe
  food coloring after it is placed into water of
  various temperatures.
• Hypothesis ?
• Materials
• food coloring
• three 250 mL beakers
• water of various temperatures (hot, room
  temperature, cold)
• clock/timer
• data table
• Procedures
• Write a hypothesis on the back of your data
  table.
• Label the beakers and fill them with 100 mL of
  hot, room temperature, and cold water.
• Place a drop of food coloring into each of the
  beakers.
• Each member of the group should rate how much the
  food coloring has diffused in the beaker over a
  ten minute period of time
• 1 small amount (1-33)
• 2 medium amount (33-67)
• 3 large amount (67-100).
• Average your results and create a line graph of
  your average data with the rating on the y-axis
  and the timed intervals on the x-axis.

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Data Table
2 Minutes 2 Minutes 2 Minutes 4 Minutes 4 Minutes 4 Minutes 6 Minutes 6 Minutes 6 Minutes 8 Minutes 8 Minutes 8 Minutes 10 Minutes 10 Minutes 10 Minutes
H R C H R C H R C H R C H R C
Member
1
2
3
4
5
Average
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Discussion Questions

1. What patterns or trends did you notice?
2. What factors could have impacted the accuracy of
   your data?
3. Did your data support your hypothesis? Explain
   your reasoning.

5
Kinetic Theory of Matter

• states that all of the particles that make up
  matter are constantly in motion ? all particles
  in matter have kinetic energy
• energy is transferred when particles collide with
  one another
• helps explain the different states of matter
• PhET

What do you think happens when a slow moving
particle is struck by a fast moving one?
6
Temperature

• the quantity that tells how hot or cold something
  is compared to a standard
• the average kinetic energy of all the particles
  in an object ? not determined by how much of a
  substance you have
• Higher average kinetic energy (particle movement)
  results in higher temperatures, while lower
  average kinetic energy (particle movement)
  results in lower temperatures
• measured using a thermometer

7
Thermometer

• an instrument for measuring temperature
• typically a thin glass tube filled with a liquid
  (alcohol or mercury)
• mercury is not typically used anymore because of
  its impact on the environment
• works because of thermal expansion
• consist of three different scales
• Fahrenheit (0F)
• Celsius (0C)
• Kelvin (K)

Why is alcohol used in thermometers instead of
water?
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Temperature Scales
Which scale is being represented by each
thermometer?
2120
1000
373
Water boils
The Kelvin scale does not have negative numbers
680
200
293
Room temperature
320
00
273
Water freezes
Fahrenheit
Celsius
Kelvin
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Converting Between Scales

• Celsius to Fahrenheit
• Fahrenheit to Celsius
• Celsius to Kelvin
• Kelvin to Celsius

50C ? 0F
0C
0F
50C
410F
700F ? 0C
0C 5 x (0F - 32) 9
5 x ( - 32) 9
0F
0C
700F
210C
100C ? K
K 0C 273
100C
283K
273
0C
K
100 K ? 0C
0C K - 273
- 273
K
0C
100 K
-1730C
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Combining Different Temperatures

• Overview
• For this activity you will mix different amounts
  of hot and cold water.
• Materials
• 3 - 250 mL beakers
• 2 - 100 mL graduated cylinder
• three Celsius thermometers
• hot and cold water
• Procedures
• Label the three beakers (H, C, M).
• Using the graduated cylinder, measure the amount
  of cold water specified by the data table and
  pour it into the beaker labeled C. Measure and
  record the temperature.
• Using the graduated cylinder, measure the amount
  of hot water specified by the table and pour it
  into the beaker labeled H. Measure and record
  the temperature.
• Predict what the temperature will be after
  combining the beakers.
• Pour the hot and cold water into the beaker
  labeled M. Measure and record the water
  temperature.
• Repeat steps 2-5 for the remaining mixtures
  specified by the data table.

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Data Table
Mixture Hot Water Temperature (0C) Cold Water Temperature (0C) Predicted Mixed Temperature (0C) Actual Mixed Temperature (0C)
100 mL hot 100 mL cold
50 mL hot 150 mL cold
150 mL hot 50 mL cold
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Questions

1. How does the temperature of the different
   mixtures compare to the original temperatures of
   the water?
2. For which mixture did your prediction come
   closest?
3. For which mixture was your prediction farthest
   off?
4. Could the temperature of the mixture (hot and
   cold) ever reach the temperature of the hot or
   cold water? Explain your reasoning.
5. Although the hot water was the same temperature
   in each beaker, the impact observed when it was
   combined with the cold water varied. Why did
   they all have a different effect?
6. What factors could have impacted the accuracy of
   your data?
7. What did you learn about mixing temperatures from
   this activity?
8. What would you predict the temperature to be if
   200 mL of hot water (1000C) is mixed with 50 mL
   of cold water (00C) ? Explain your reasoning.

13
Heating and Cooling a Metal Strip

1. Plug in the hot plate and allow it to heat up for
   3-5 minutes.
2. Have a conversation with the members of your
   group regarding what you think will happen once
   you heat and cool the metal strip.
3. Using the hot plate, heat the metal strip with
   the printed side facing upward. It is not
   necessary to touch the metal strip on the hot
   plate.
4. Take note of what you observe as the metal strip
   is heated with the hot plate.
5. Allow the strip to cool for a few minutes.
6. Gently rub the metal strip on an ice cube with
   the printed side facing upward.
7. Take note of what you observe as the metal strip
   it is being cooled with the ice.

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Discussion Questions

1. What observations did you make after putting the
   metal strip over the hot plate? Be specific!!!
2. Why/how did this happen?
3. What observations did you make after rubbing the
   metal strip on the ice cube? Be specific!!!
4. Why/how did this happen?
5. What do you think would have happened if it was
   heated or cooled to a greater degree?

The metal strip is actually know as a bimetal
strip.
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Thermal Expansion

• the increase in volume of a substance due to an
  increase in temperature the particles
  themselves DO NOT expand
• as a substance gets hotter the particles move
  faster and spread out
• most matter expands when its heated and
  contracts when its cooled
• Exception - water actually expands as it cools
  from 40C to 00C
• different substances expand at different rates
• gases generally expand or contract more than
  liquids, and liquids expand or contract more than
  solids
• Example
• Bimetal strips in thermostats

As the particles spread out, the volume of a
substance increases. What happens to the
substances density?
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Thermal Expansion Contraction(A closer look)
Expansion
Contraction
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Applications of Thermal Expansion and Contraction

• Try to apply and/or explain the concepts of
  thermal expansion and contraction as they pertain
  to the following examples.
• expansion joints in bridges or sidewalks
• thermometers
• hard to open jar lid
• railroad tracks and train derailments
• telephone/power lines
• potholes
• objects filled with gas (tire, balloon, athletic
  ball, etc.)

What are some personal examples or experiences
with thermal expansion and contraction?
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Heat

• flow or transfer of energy from an object at a
  higher temperature to an object at a lower
  temperature until thermal equilibrium is reached
• matter does not have heat it has thermal energy
• typically expressed in units of joules (J) and
  calories (cal)
• Calories is really a kilocalorie and represents
  food energy
• 4.187 joules 1 calorie
• scientists believed that heat was an invisible,
  weightless fluid capable of flowing ?caloric
• Count Rumford (Benjamin Thompson) challenged the
  idea of caloric when he discovered that heat was
  being produced when holes were drilled into
  cannon barrels
• 3 types of heat transfer conduction, convection,
  radiation

Why does an ice cube feel cold while a paper cup
filled with coffee feels hot?
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Using the Conductometer

1. Place an equal amount of wax in the divots of
   each rod (A,B,S,N,C).
2. Light the candle.
3. With the wax filled divots facing upward, place
   the central heating disk directly over the
   candle.
4. Observe the order in which the wax melts.

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Discussion Questions

1. What is the order in which the wax melts.
2. What impacted how quickly the wax melted in each
   rod?
3. What factors could have impacted the accuracy of
   your results?

1. Copper (C)
2. Aluminum (A)
3. Brass (B)
4. Steel (S)
5. Nickel (N)

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Specific Heat Capacity

• the amount of energy needed to change the
  temperature of 1 kg of a substance by 10C
• how easily substances change temperatures
• increases as the size of the particles that make
  up the substance increase
• the higher the value ? the more energy and the
  longer it takes to heat up or cool down
• i.e. with a specific heat of 1.00 cal/g?0C,
  water (0.93 cal/g?0C for ocean water) will take
  longer to heat up and cool down compared to
  copper which has a specific heat value of 0.09
  cal/g?0C
• can be used to help calculate heat lost or gained
  by a substance
• formula MC?T

Explain how/why bodies of water in our area are
warmer towards the end of the summer compared to
the beginning.
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Table of Specific Heat Values
Substance Specific Heat (cal/g?0C) Specific Heat (J/kg?0C)
Air 0.25 1,046
Aluminum 0.22 899
Copper 0.09 387
Glass 0.20 837
Ice (-200C to 00C) 0.50 2,090
Iron 0.11 448
Mercury 0.03 138
Ocean Water 0.93 3,894
Water 1.00 4,187
Wood 0.42 176
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Conduction

• transfer of thermal energy through a substance,
  or from one substance to another by direct
  contact of particles
• takes place in solids, liquids, and gases, but
  takes place best in solids because the particles
  of a solid are in direct contact with each other

Unfortunately for someone, after being touched,
the heat will transfer from the iron to the hand.
What are some other real-life examples where
heat is transferred by conduction?
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Conductors and Insulators

• Conductors
• substances that conduct thermal energy well
• particles are close together
• different metals are common conductors

• Insulators
• substances that do not conduct thermal energy
  well ? they delay heat transfer
• particles are far apart
• different plastics are common insulators

What are some common conductors and insulators?
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Convection

• transfer of thermal energy through fluids
  (liquids or gases) by means of up and down
  movements called convection currents
• the circular motion of liquids or gases due to
  density differences that result from temperature
  differences

As the air gets heated by the flame, the
particles move faster and spread out. This
increases the volume of the air inside the
balloon, which lowers the density. This decrease
in density causes the balloon to rise.
Sea and land breezes result from uneven heating
of the Earths and the resulting convection
currents. Explain how this happens.
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Radiation

• transfer of thermal (radiant) energy as
  electromagnetic waves, such as visible light or
  infrared waves
• energy can be transferred through matter or
  empty space
• darker objects absorb more radiant energy than
  lighter objects

Notice how the visible light from the sun travels
through space and heats the Earth.
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Temperature vs. Heat vs. Thermal Energy
Temperature Thermal Energy Heat
a measure the average kinetic energy of all the particles in an object the total energy of the particles in a substance the transfer of energy between objects that are at different temperatures
expressed in degrees Fahrenheit, Celsius, or Kelvin expressed in joules expressed in joules or calories
does not vary with the mass of a substance varies with the mass and temperature of a substance varies with the mass, specific heat capacity, and temperature change of a substance
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Calculating Heat Sample Problem

• How many joules are needed to raise the
  temperature of 100 kilograms of copper from 10 ?C
  to 100 ?C? The specific heat of copper is 387
  J/kg?C.

Take the difference between 100C and 1000C
Q mc?T
specific heat
heat
mass
change in temperature
Heat
(100 kg)
(90 ?C)
Heat 3,483,000 J