heat section 1 © houghton mifflin harcourt publishing company preview section 1 temperature and...

Heat Section 1

© Houghton Mifflin Harcourt Publishing Company

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Section 1 Temperature and Thermal Equilibrium

Section 2 Defining Heat

Section 3 Changes in Temperature and Phase

Heat Section 1


The student is expected to:TEKS

6E describe how the macroscopic properties of a

thermodynamic system such as temperature, specific

heat, and pressure are related to the molecular level

of matter, including kinetic or potential energy of

atoms

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What do you think?

• Suppose you have two cups of water. One is hot and the other is cold. – How is the cold water different from the hot water?

• Describe the motion of the molecules in each.

– What changes would occur if the hot water was changed into steam?

• What are the common scales used to measure temperature?– When is each scale generally used?– All scales use degrees to measure temperature.

Which scale has the largest degrees? Explain.

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Temperature

• Temperature measures the average kinetic energy of the particles.– Average speed is used because all particles do not

have the same speed, and speeds change as the particles collide.

• Internal energy is the energy a substance has due to the motion of the particles (kinetic energy) and the position of the particles (potential energy).

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Click below to watch the Visual Concept.

Visual Concept

Forms of Internal Energy

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Temperature

• Do thermometers change the temperature of the substance being measured? – If so, how?– How can you minimize the problem?

• Temperature must be measured when thermal equilibrium is reached.

• Always read a thermometer after it has stopped rising or falling.– At this point, equilibrium has been reached between

the thermometer and the substance.

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Visual Concept

Thermal Expansion

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Thermometers

• The expansion of mercury changes the reading in this thermometer.

• How does such a small change in the volume of the mercury (see circled segments) result in such a large rise inside the thermometer?

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Thermometers

• Calibration depends on fixed temperatures.• Three common temperature scales used:

– Fahrenheit for weather and medicine (U.S.)– Celsius for work in science– Kelvin or absolute for many scientific laws

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Comparison of Temperature Scales

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The Absolute Temperature Scale

• What is meant by absolute zero?– Absolute zero = 0 K

• Suppose the pressure and temperature of a gas are plotted as shown, and the graph is extrapolated to 0 K. What does this suggest about P at absolute zero (-273.15°C or 0 K)?– P = 0 at absolute zero

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Temperature Conversions

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Classroom Practice Problems

• One day it was -40°C at the top of Mont Blanc and -40°F at the top of Mount Whitney. Which place was colder?– Answer: Neither (-40°C = -40°F)

• What is the Fahrenheit temperature equivalent to absolute zero?– Answer: -459.67°F

• What is the Celsius temperature on a hot summer day when the temperature is 100. °F?– Answer: 37.8°C

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Now what do you think?

• Suppose you have two cups of water. One is hot and the other is cold. – How is the cold water different from the hot water?

• Describe the motion of the molecules in each.

– What changes would occur if the hot water was changed into steam?

• What are the common scales used to measure temperature?– When is each scale generally used?– All scales use degrees to measure temperature.

Which scale has the largest degrees? Explain.

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atoms

6F contrast and give examples of different processes

of thermal energy transfer, including conduction,

convection, and radiation

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What do you think?

• Internal energy is the energy due to the kinetic and potential energy of the particles.

– Does the ice water or an equal quantity of hot chocolate have greater internal energy? Why?

– Which has more internal energy, a gallon of cold water or a drop of hot chocolate?

– How will the internal energy of the water and hot chocolate change over time?

• How will this change occur?

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Internal Energy and Heat• Internal Energy (U) is the energy contained

within the particles of a substance.• Heat (Q) is the internal energy transferred

between objects.– Heat always moves from a higher-temperature

object to a lower-temperature object.– The rate of transfer depends on the difference in

temperature.• The greater the temperature difference, the greater the rate

of energy transfer (if other factors are equal).

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Internal Energy and Heat• Which way does heat flow if you place a warm

canned beverage in cold water? • How does this occur, on a molecular level?

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Visual Concept

Temperature and Heat

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Heat has Units of Energy (joules)

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Heat Transfer

• In what three ways can internal energy be transferred from a hot object to a colder object?– Conduction is the transfer of heat through a substance

by molecule to molecule contact.• Metals are good conductors.• Styrofoam is a good insulator.

– Convection is the transfer of energy by the movement of a fluid.

• Hot air in a room rises and cold air moves in to replace it.

– Radiation is the transfer of energy by electromagnetic waves.

• No matter is transferred, only energy.

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Visual Concept

Comparing Convection, Conduction, and Radiation

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Heat and Work

• Work can be changed into internal energy (U).– Rub your hands together and you’ll feel the increase in

internal energy produced by your work.– Pull a nail from a piece of wood and the nail is hot.

• Mechanical energy (PE + KE) is conserved when there is no friction.

• Total energy, including internal energy, is always conserved.

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Energy Conservation

• Any loss of one type is balanced by a gain in the other types of energy.

• Predict the sign (+, -, or 0) for the change in each quantity when:– A child slides down a plastic playground slide– A car applies the brakes to stop on a level road

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– Does the ice water or an equal quantity of hot chocolate have greater internal energy? Why?

– Which has more internal energy, a gallon of cold water or a drop of hot chocolate?

– How will the internal energy of the water and hot chocolate change over time?

• How will this change occur?

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atoms

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What do you think?

• What property of water makes it so useful as a coolant in automobiles, nuclear reactors, and other machinery? • How does it differ from other liquids regarding its

ability to cool substances?

• Why do you feel cool when getting out of a warm swimming pool on a hot day?• How do you feel if it is windy out? Why?• How do you feel if it is an indoor pool? Why?

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Specific Heat Capacity• Specifc heat capacity (cp) measures the amount of heat

required to raise the temperature by 1°C for 1 kg of a substance.– It is different for every substance.

• SI Units: J/kg•°C

• Alternate form of this equation: Q = cpmT

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• Suppose each metal shown above absorbs 100 J of energy. – Which will show the greatest increase in temperature? the least?– How does water compare to iron with regard to heat capacity?

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Calorimetry

• Calorimetry is a problem-solving approach to heat transfer problems.– Conservation of energy

– Qgained = -Qlost

• A calorimeter is an insulated cup with water used for the experiment.– Ignore heat gained or lost by

the cup, as it is small.

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Classroom Practice Problem

• In a student’s experiment, a 0.125 kg metal ball is placed in a calorimeter filled with 0.150 kg of water at 21.0°C. The initial temperature of the ball is 98.5°C. After reaching equilibrium, the temperature is 27.3°C. Find the specific heat capacity of the metal and use the table to determine the type of metal.– Answer: 444 J/kg•°C , very close to iron

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Classroom Practice Problem

• A bathtub has 20.0 kg of water at 60.0°C and the bather wants the temperature to be 30.0°C. How much 20.0°C water must be added to the bath water to achieve the desired temperature?

– Answer : 60.0 kg

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Latent Heat

• Latent heat is heat gained or lost during phase changes.– When substances melt, freeze, boil, condense, or

sublime, the temperature does not change during the phase change.

– Heat absorbed changes the potential energy of the particles.

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Visual Concept

Latent Heat

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• Heat of vaporization (Lv) is the heat required to change 1 kg of a substance from a liquid to a gas.– Which graph segment represents this?

Latent Heat• Heat of fusion (Lf) is

the heat required to melt 1 kg of a substance.– Also equals the

heat released when 1 kg freezes

– Which graph segment represents this?

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Latent Heats of Fusion and Vaporization

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• What property of water makes it so useful as a coolant in automobiles, nuclear reactors and other machinery? • How does it differ from other liquids regarding its

ability to cool substances?

• Why do you feel cool when getting out of a warm swimming pool on a hot day?• How do you feel if it is windy out? Why?• How do you feel if it is an indoor pool? Why?

heat section 1 © houghton mifflin harcourt publishing company preview section 1 temperature and...

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