Transcript 21.7 The High Specific Heat Capacity of Water

Thermal Energy
Internal energy: energy
of the moving particles
that compose matter
Starter 3 Thermal Energy
Transfer
• Read Ch. 22.1-22.3
• Fold a piece of notebook paper to form
three columns
– Head each column with one of the three ways
that thermal energy can be transferred
– Define each
– List three main points from the reading for
each thermal energy transfer process
• On the back of the paper, prepare an
example illustrating how each transfers
heat
Today’s Key Terms and Ideas
•
•
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Thermal Energy
Kinetic Theory
Heat
Thermal Equilibrium and heat transfer
Kinetic Theory as it relates to expansion
and contraction
• Hot vs. cold
Physics and Particles
• Particle is a general term used to describe
molecules, atoms and sub-atomic particles
21.1 Temperature
The higher the temperature of a substance, the
faster the motion of its molecules.
This is also referred to as the Kinetic Theory—
a) all matter is made of atoms and molecules that
are moving.
b) The higher the temperature, the faster the
particles move.
c) Given the same temperature, heavier particles
move slower than lighter particles.
Matter is
changing
state
solid
melting
freezing
liquid
evaporation
condensation
gas
Particle speed is
increasing
Increasing
Avg. KE
Increasing
Temp.
21.1 Temperature
Temperature and Kinetic Energy
Temperature is related to the average kinetic energy
of the atoms and molecules in a substance.
The faster the molecules move, the
greater
______________
the temperature and the
greater
_____________
the average kinetic energy and the
greater
__________
the particle speed.
21.2 Heat
1. Heat is the quantity of thermal energy transferred
2. Heat always flows from a substance with a higher
temperature to a substance with a lower
temperature.
3. Heat flows only when there is a difference in
temperature.
4. Heat units are calories or joules.
21.2 Heat
Just as water will not flow
uphill by itself, regardless
of the relative amounts of
water in the reservoirs,
heat will not flow from a
cooler substance into a
hotter substance by itself.
hotter
Entropy!
Flow from higher
to lower energy
state.
colder
21.2 Heat
What causes heat to flow?
A difference in temperature
between objects in thermal contact.
21.4 Internal Energy
When a substance takes in or gives off heat, its
internal energy changes.
21.3 Thermal Equilibrium
What happens when a warmer
substance comes in contact with a cooler
substance?
• Heat flows between two objects of different
temperature until they have the same
temperature.
• The loss of thermal energy from the warmer
object equals the gain of thermal energy for
the cooler object
21.8 Thermal Expansion
Most forms of matter—solids, liquids, and gases—
expand when they are heated and contract when they
are cooled.
21.8 Thermal Expansion
When the temperature of a substance is increased,
its molecules jiggle faster and normally tend to
move farther apart.
This results in an expansion of the substance.
• Gases generally expand or contract much
more than liquids.
• Liquids generally expand or contract more
than solids.
Starter Question #2
How does a thermometer work?
The kinetic theory be used to explain expansion
and contraction of materials when the
temperature of the material changes.
As the temperature rises, heat is transferred from
the surroundings to the liquid inside the
thermometer and the molecules that compose
the liquid vibrate faster. This causes the liquid
to expand and rise.
As the temperature falls, heat is transferred away
from the liquid inside to the surroundings and
the molecules that compose this liquid slow
down. This causes the liquid to contract.
• The liquid in the thermometer stops rising
or falling when thermal equilibrium is
reached (no more heat flow!)
Air temperature = Liquid temperature
21.6 Specific Heat Capacity
Do copper, clay and water have the same
chemical composition?
•No. Copper is composed of Cu atoms and water is
composed of H2O molecules. Clay is a complex
silicate.
•The difference in chemical composition influences
how copper, clay and water respond when heat is
transferred.
The specific heat capacity of a substance is the quantity of heat
required to raise 1 g of a substance by 1 degree Celsius.
21.6 Specific Heat Capacity
A substance with a high specific heat
capacity can absorb a large quantity of
heat before it will raise in temperature
(water has a high specific heat).
A substance with a low specific heat
requires relatively little heat to raise its
temperature (copper has a low specific
heat).
21.6 Specific Heat Capacity
highest
lowest
21.6 Specific Heat Capacity
think!
Which has a higher specific heat capacity—water or sand?
Explain.
21.6 Specific Heat Capacity
think!
Which has a higher specific heat capacity—water or sand?
Explain.
Answer:
Water has a greater heat capacity than sand. Water is much
slower to warm in the hot sun and slower to cool at night.
Sand’s low heat capacity, shown by how quickly it warms in
the morning and how quickly it cools at night, affects local
climates.
Good conductors have a low specific heat capacity!
21.6 Specific Heat Capacity
A gram of water requires 1 calorie of energy to raise the
temperature 1°C.
It takes only about one eighth as much energy to raise the
temperature of a gram of iron by the same amount.
The capacity
of a
substance to
store heat
depends on
its chemical
composition.
21.6 Specific Heat Capacity
6.
What is the difference between a
substance with a high specific heat and a
low specific heat capacity?
• Substances with a low specific heat (e.g.,
metals) need very little heat to raise
temperature
– Good conductors, not good absorbers, do not
hold onto heat well
• Substances with a high specific heat need
a large quantity of heat to raise
temperature.
– Poor conductors, good absorbers, store and
hold onto heat well
7. How does the specific heat of water help
to moderate climate?
• During the summer, surrounding air is
cooled by the water and keeps the coast
cooler than the intercontinental locations.
• During the winter, the surrounding air is
warmed by the water and keeps the coast
warmer than the intercontinental locations.
21.7 The High Specific Heat Capacity of Water
The property of water to resist changes in
temperature improves the climate in many places.
21.7 The High Specific Heat Capacity of Water
Water has a high specific heat and is transparent, so it takes
more energy to heat up than land does.
21.7 The High Specific Heat Capacity of Water
Water’s capacity to store heat affects the global climate.
Water stores and hold heat well because of its high specific
heat.
•Gulf Stream brings warm water northeast from the Caribbean.
•It holds much of its thermal energy long enough to reach the
North Atlantic off the coast of Europe.
•As it cools, the energy released is carried by the prevailing
westerly winds over the European continent.
The Gulf Stream brings warm winters to Ireland and the prevailing winds off the
Atlantic carry with them rain. It means grass can grow almost all year round —
creating the lush sweeping pastures of the Emerald Isle. Today they make up 93
percent of all farmland. No other country in Europe has quite as much grass as
Ireland.
21.7 The High Specific Heat Capacity of Water
Climate of Europe
Look at a world globe and notice the high latitude of Europe.
Both Europe and Canada get about the same amount of the
sun’s energy per square kilometer.
Marine Climate
Continental Climate
Cork
Edmonton
Same insolation
angle, different
climate due to
proximity to water
and the warming
effect from the
Gulf Stream
http://www.sampleireland.com/weather-in-ireland-year-round.html
21.7 The High Specific Heat Capacity of Water
Climate of America
On the west coast, air moves from the Pacific Ocean to the
land.
• In winter, the water warms the air that moves over it and
warms the western coastal regions of North America.
• In summer, the water cools the air and the western
coastal regions are cooled.
The central interior of a large continent usually
experiences extremes of temperature.
Land, with a lower specific heat capacity, gets hot
in summer but cools rapidly in winter.
8. In which three ways can the thermal
energy (or heat) of a substance be
transferred?
Heat can be transferred by
conduction, by convection,
and by radiation.
22.1 Conduction
In conduction, collisions between particles
transfer thermal energy, without any overall
transfer of matter.
22.1 Conduction
Heat from the flame causes atoms and free
electrons in the end of the metal to move faster
and jostle against others. The energy of vibrating
atoms increases along the length of the rod.
22.2 Convection
In convection, heat is transferred by
movement of the hotter substance from
one place to another.
22.2 Convection
Convection occurs in all fluids.
a. Convection currents transfer
heat in air.
Hot, less dense fluid rises in the presence
of cooler, more dense fluid.
22.2 Convection
Convection occurs in all fluids.
a. Convection currents transfer
heat in air.
b. Convection currents transfer
heat in liquid.
When fluid particles at the bottom of the
pan begin to vibrate faster, they expand
and decrease in density, making the hotter
fluid more buoyant.
22.3 Radiation
In radiation, heat is transmitted in the form of radiant
energy, or electromagnetic waves.
22.3 Radiation
Most of the heat from a fireplace goes up the chimney by
convection. The heat that warms us comes to us by radiation.
• Radiation is caused by moving electrons
or charged particles in matter. The faster
the particles move, the higher the
frequency of the electromagnetic radiation.
22.3 Radiation
a. Radio waves send signals through the air.
22.3 Radiation
a. Radio waves send signals through the air.
b. You feel infrared waves as heat.
22.3 Radiation
a. Radio waves send signals through the air.
b. You feel infrared waves as heat.
c. A visible form of radiant energy is light waves.
11. What happens to the frequency of
radiant energy as the temperature of the
substance increases or decreases?
• The frequency of radiant energy increases
as the temperature of the substance
increases.
http://mail.jsd.k12.ca.us/bf/bflibrary/images/electromagnetic-spectrum.jpg