Chapter 16 notes
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Chapter 16
Thermal Energy and Heat
Thermal Energy and Matter
Heat: is the transfer of thermal
energy from one object to another
due to a difference in temperature
Heat flows from:
HOT COLD
Cold: losing heat energy
Hot: gaining heat energy
Kinetic Theory- all matter is made of
particle (atoms, molecule, ions).
These particles are always in random
motion.
Higher Temp = higher kinetic = faster
motion
Temperature: is how hot or cold an
object is compared to some reference
point
Examples:
Outside Temperatures
Temperature of buildings 70.0’F
Runoff Water Temp. 35-42’F
Body Temp. 98.6’ F
Thermometer: tool used to measure
temp. 3 different scales ‘C ‘F K
Mercury expands as the thermometer
gains heat (UP)
Mercury contracts as the
thermometer loses heat (DOWN)
Formulas pg 255 C F, F C
Thermal energy: depends on mass,
temperature and phase of an object.
Thermal energy is caused by the
movement of atoms and molecules
(friction)
Mass: greater mass = greater thermal e.
More mass = longer to heat up & cool down
Temp. greater temp = greater thermal e.
Greater SpecificHeat = Greater thermal E
Phase: depends on amount of thermal E.
Solid:
Liquid:
Gas:
Plasma: most heat energy
The States of Matter, Molecular Stickiness, and Thermodynamicsitl.chem.ufl.edu
Thermal Expansion: occurs because
particles of matter tend to move faster and
spread out as temperature increases
INCREASE HEAT = INCREASE SIZE
DECREASE HEAT = DECREASE SIZE
Ex. Joints in side walks (celotex), joints in
bridges, thermostats in homes, Thermometer
Balloon Demo: expanded as we added heat
Specific Heat: a physical property that
describes how a substance absorbs heat
Different substances absorb heat at
different rates
The lower a material’s specific heat, the
more its temp. will increase as heat is
added. (heats & cools faster)
Metals: low specific heat
Nonmetals: high specific heat
Specific Heat of Common Materials
Water =
Plastic =
Air =
Iron =
Silver =
4.18
J/g-’C
1.8 to 2.1 J/g-’C
1.01
J/g-’C
.449
J/g-’C
.225
J/g-’C
Measuring Heat Changes
Calorimeter: is an instrument used to
measure changes in a material’s heat
Closed container that holds water,
thermometer, stirring rod
Used to calculate specific heat
Used to calculate # of calories in food
Picture on next slide and in book
http://www.agro.cmu.ac.th/department/fe/equip
http://www.agro.cmu.ac.th/departme
nt/fe/equip_file/031_1.jpg
http://www.agro.cmu.
ac.th/department/fe/e
quip_file/031_1.jpg
http://research.chem.psu.edu/mallouk/ilab/models.htm
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16.2 Heat & Thermodynamics
There are 3 ways that thermal energy
is transferred from one object to
another
Conduction
Convection
Radiation
Conduction: is a heat transfer when 2
objects are touching (direct contact)
There is NO transfer of matter
Conduction works fastest with:
Solids Liquids Gases
The particles of liquids and gases are
farther apart than solids, therefore
heat is not transferred as quickly
Thermal Conductors: are materials
that allow heat and electricity to pass
through them easily
Metals
Copper wire for electrical circuits, gold
wire in spaceships, pots & pans
Low specific heat values
Thermal insulators: are materials that
DO NOT allow heat and electricity to
pass through them easily
Non-metals
Wood, plastic, air, glass, fiberglass
Protect items from heat and electricity
High specific heat values
Convection: heat transfer that takes place
in fluids (liquids and gases)
HOT AIR/WATER RISES
Convection Currents: currents in liquids or
gases, these currents transfer thermal
energy (caused by difference in density)
Ex. Pavement, beaker of hot water,
ocean currents, weather patterns, wind
Radiation: is the transfer of thermal
energy (heat) by waves through
space
Radiation happens through air and
empty space
Ex. Sun, wood burning stove,
fireplace, candles
All objects radiate thermal energy
1st Law of Thermodynamics: states
that thermal energy is conserved
Heat energy can’t be created nor
destroyed
Heat energy can only be transferred
and converted
2nd Law of Thermodynamics: states
that heat CAN flow from COLDER
objects to HOTTER objects, ONLY if
work is done.
Ex. refrigerator, freezer, A.C.
Freon: refrigerant liquid/gas that
is used in the cooling process
(cars)
ENTROPY:
The measure of how dispersed the
energy is.
3rd Law of Thermodynamics: states
that absolute zero CAN’T be reached
Absolute Zero: is the coldest possible
temperature where molecular (atoms)
motion stops
Absolute Zero = 0 K
Using Thermal Energy
Heating Systems:
Forced-air: fuel heats air and fan pushes
through the building. Cold air returns
Radiator:hot water or steam heat
through radiation to the air. Uses a
boiler to heat water
Electric: electricity heats coils in floor or
ceiling by conduction.