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Conceptual

Physical

Science

6th Edition

Chapter 7: 7.5-7.9

HEAT TRANSFER AND

CHANGE OF PHASE

Outline

• Conduction• Convection• Radiation• Newton’s Law of Cooling

• Climate Change and the Greenhouse Effect

• Heat Transfer and Change of Phase• Boiling• Melting and Freezing• Energy and Change of Phase

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Heat versus Temperature

Temperature

• A measure of hotness or coldness of an object

• Based on average molecular kinetic energy

Heat

• Based on total internal energy of molecules

• Doubling amount at same temperature doubles heat

Definition• A measure of the internal energy

that has been absorbed or transferred from another object

• Two related processes– “Heating” = increasing internal

energy

– “Cooling” = decreasing internal energy

Heat Flow

Three mechanisms of heat transfer due to a

temperature difference

1. Conduction

2. Convection

3. Radiation

Natural flow is always from higher temperature

regions to cooler ones

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Radiation

Radiation• Transfer of energy via electromagnetic waves

that can travel through empty space

Heat Transfer: Radiation

Wavelength of radiation is related to the frequency of vibration.

Frequency Energy

High-frequency vibrations short waves

Low-frequency vibrations long waves

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Radiation

Emission of radiant energy• Every object above absolute

zero radiates

• From the Sun’s surface comes light, or solar radiation

• From the Earth’s surface is terrestrial radiation in the form of infrared waves below our threshold of sight

Climate Change and the Greenhouse Effect

Greenhouse Effect• Named for a similar temperature-raising effect

in florists’ greenhouses

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Climate Change and the Greenhouse EffectClimate Change• Energy absorbed from the Sun• Part reradiated by Earth as longer-wavelength

terrestrial radiation

If Earth radiated more energy than it absorbs from the Sun, Earth’s average temperature would

A. decrease.

B. increase.

C. likely not change.

D. None of these.

Climate Change and the Greenhouse Effect

CHECK YOUR NEIGHBOR

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Which body emits radiant energy into space?

• Sun.

• Earth.

• Both of the above.

• None of the above.

Compared with radiation from the Sun, terrestrial radiation has a lower

• wavelength.

• frequency.

• Both of the above.

• Neither of the above.

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Fact: Atmospheric CO2

levels are increasing

Dr. William Blair, Johns Hopkins University

Greenhouse Gases

• Water Vapor H2O

• Methane CH4

• Carbon Dioxide CO2

▪A trace constituent, but very

effective at trapping heat.

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US Energy Resources

We get 80% of our energy from oil, coal, and natural gas (methane)

These are fossil fuels

~80% of our energy comes from fossil fuels

http://www.eia.gov/totalenergy/data/annual

gasoline (refined oil) combustion:

2 C8H18 + 25 O2 → 16 CO2 + 18 H2O + KE

natural gas (methane) combustion:

CH4 + 2 O2 → CO2 + 2 H2O + KE

coal combustion:

C + O2 → CO2+ KE

Fossil Fuel Combustions

• CO2 is a greenhouse gas - global warming

• note that gasoline produces the most CO2 per combustion

• coal/natural gas produce less CO2 and is also cheaper BUT you don’t get as

much horsepower from coal as from gasoline – we are willing to pay more

for power

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Climate Change and the Greenhouse Effect

Climate Impacts

Warmer sea temperatures…• cause stronger storms and affect

atmospheric and sea circulation patterns.• Can cause droughts in some areas and

excessive rainfall in others.• Add to the rise in sea level.

– Warm water has a larger volume.

Katrina 2005

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Greenhouse Effect

Mt. Pine Beetle damage, Montana

(NYT, 11/17/08)

Evidence of Warming

Larsen B Ice Shelf, Antarctica, 2006

Glacier National Park, Montana

19382003

North Polar

Ice 2007

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What’s So Good About GDP?

• GDP per capita is a measure of a country’s standard of

living

• to enjoy this kind of lifestyle, a country must have

energy resources

• without energy resources, even basic needs are at risk

• high GDP per capita means a luxurious/convenient lifestyle

• this is why energy is an important societal and political issue

Source: US Department of Agriculture

Global Sustainability

• U.S. per capita energy consumption (hence, CO2production) is 32x that of the developing world.– The U.S. consumes energy at a rate comparable

to 10 BILLION people in the developing world!• If the developing world rises to our level of

consumption, the energy needs are immense.– If they do it with fossil fuels, we are toast!

• Our level of energy consumption is not sustainable and is not just by the world’s standards.

>> We must reduce our consumption and help the rest of the world cope with their needs.

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BALANCE

Apollo 11, July 1969

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Venus - Our Twin Planet?*

• Closest planet to earth.

• Nearly the same size as earth, but

• CO2 atmosphere 100x denser than earth’s.

• Surface temp 900 degrees F.

• Example of “Runaway” Greenhouse effect.

Dr. William Blair, Johns Hopkins University

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