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THERMAL ENERGY & MATTER

DEMONSTRATION

• Food Coloring and Water

WHAT IS HEAT?

• The transfer of thermal energy from one object to another because of a temperature difference

• Flows spontaneously from hot objects to cold objects

TEMPERATURE

• Related to the average kinetic energy of the particles in an object due to their random motions through space

KINETIC THEORY OF MATTER

• Matter is made up of particles (or atoms) that are in constant motion

HEAT UP• Particles gain kinetic

energy, move faster, average kinetic energy of all particles increases

COOL DOWN• Particles move slower,

average kinetic energy of all particles decreases

DICE GAME

• You are now a particle of matter…

THERMAL ENERGY

• The total potential and kinetic energy of all the particles in an object

• Depends on the mass, temperature and phase (solid, liquid, or gas) of an object

BALLOON DEMONSTRATION

THERMAL CONTRACTION

• As temperature decreases, particles move more slowly

• Slower moving particles have less average kinetic energy• This means that the particles collide less often and exert

less force on one another

CAN DEMONSTRATION

THERMAL EXPANSION

• Occurs when particles of matter move farther apart as temperature increases

• Gases expand more than liquids• This is because the forces of attraction among particles in

a gas are weaker

• Liquids expand more than solids

MAKING THERMOMETERS

• Now, your group will make a thermometer using the materials provided in order to see thermal expansion and contraction first hand.

AN IMPORTANT EXCEPTION

• Water• Water expands as it freezes, unlike most other

substances • This is due to something called Hydrogen Bonding, which

we will learn more about next semester

• This has important corollaries in everyday life… Can you think of any?

SPECIFIC HEAT

• The amount of heat needed to raise the temperature of one gram of a material by one degree Celsius

• The higher a material’s specific heat, the less its temperature rises when a given amount of energy is absorbed by a given mass

• Different materials heat up at different rates!

WATER

• Water has a high specific heat• This means that it takes a lot of thermal energy to

change temperature of water

• Why?• Hydrogen Bonding (more to come next semester)

• Consequences of Waters high specific heat?• Weather (daily and long term)

MEASURING HEAT CHANGES

• Heat flows from hotter objects to cooler objects until both objects reach the same temperature

• A calorimeter is a device that can be used to measure changes in thermal energy

HEAT TRANSFER

• Three Methods• Conduction• Convection• Radiation

CONDUCTION

• Transfer of thermal energy with no overall transfer of matter

• Occurs within a material or between materials that are touching

• Particles bump into one anther and transfer kinetic energy to one another

IN WHICH PHASE OF MATTER DOES CONDUCTION OCCUR MOST SLOWLY? WHY?

ANSWER

THERMAL CONDUCTORS

• Material that conducts thermal energy well

• Metals tend to be good conductors• Example: Pots, pans, & over racks are all made of metal

• Thermal conductors don’t have to be “hot”• Tile vs. Wood• Tile feels colder because it transfers thermal energy rapidly

away from your skin

THERMAL INSULATORS

• A material that transfers thermal energy poorly• Example: Wood, plastic

• Air is a good insulator• Example: Double-paned windows have an air space

between two sheets of glass; this slows conduction to reduce heat loss in the winter and to keep heat out during the summer

• Other examples?

CONVECTION

• The transfer of thermal energy when particles of a fluid move from one place to another

• Thermal energy is transferred by the mass movement of matter

• Convection Current• Occurs when a fluid circulates in a loop as it alternately

heats up and cools down

• Important in natural cycles like ocean currents, weather systems and the movement of hot rock in Earth’s interior

RADIATION

• The transfer of energy by waves through empty space

• How is radiation different than convection and conduction?• It does not require matter as a medium of transfer

• Common Examples• The sun heats the earth• Heat lamps used in restaurants to keep food warm

RADIATION (CONTINUED)

• All objects radiate energy

• As temperature of an object increases, the rate at which it radiates energy increases

THERMODYNAMICS

• The study of conversions between thermal energy and other forms of energy

FIRST LAW

• Energy is always conserved

• Energy can be converted into different forms, but it is never created nor destroyed

SECOND LAW

• Thermal energy can flow from colder objects to hotter objects ONLY if work is done on the system

• Example: A refrigerator• A refrigerator moves heat thermal energy from the inside

refrigeration compartment to outside of the refrigerator

HEAT ENGINES

• Any device that converts heat into work• In other words, a device that uses heat to “move”

• No heat engine is 100% efficient• The heat engine does not convert all of the heat into

work, some heat is lost to t he surrounding environment (called Waste Heat)

• Fun Fact• The universe is continuously becoming less ordered due

to wasted energy!

THIRD LAW

• Absolute Zero cannot be reached

• Absolute Zero• 0 Kelvin, the theoretical lowest possible temperature• At this temp. all matter would stop moving (which means

that the thermal energy of atoms would disappear!)

• What is Absolute Zero?

THERMAL EQUILIBRIUM

• Higher temperature objects will transfer thermal energy to colder temperature objects

• The objects will approach the same temperature, and then (in the absence of heat loss or gain from other objects) they will maintain a constant temperature

• Example of Student Graph

1 2 3 4 5 6 7 8 9 10 11 12 130

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The Transfer of Heat from Flasks to Beakers

Temperature of water in flask (◦C)Temperature of water in beaker (◦C)

Time (minutes)

Tem

pera

ture

(◦C

)