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 = 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

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/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

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.