Chapter 16
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Transcript of Chapter 16
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Chapter 16
Thermal Energy and Heat
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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
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Kinetic Theory- all matter is made of particle (atoms, molecule, ions). These particles are always in random motion.
Higher Temp = higher kinetic = faster motion
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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
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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
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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
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Phase: depends on amount of thermal E. Solid: Liquid: Gas: Plasma: most heat energy
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The States of Matter, Molecular Stickiness, and Thermodynamicsitl.chem.ufl.edu
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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
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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
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Specific Heat of Common Materials Water = 4.18 J/g-’C Plastic = 1.8 to 2.1 J/g-’C Air = 1.01 J/g-’C Iron = .449 J/g-’C Silver = .225 J/g-’C
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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
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http://www.agro.cmu.ac.th/department/fe/equip
http://www.agro.cmu.ac.th/department/fe/equip_file/031_1.jpg
http://research.chem.psu.edu/mallouk/ilab/models.html
http://www.agro.cmu.ac.th/department/fe/equip_file/031_1.jpg
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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
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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
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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
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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
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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
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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
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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
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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)
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ENTROPY:
The measure of how dispersed the energy is.
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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
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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.