Chapter 6, Section 7

Laws of Thermodynamics: Too Hot, Too Cold, Just Right

April 27, 2011HW: 6.7 PTG, pg. 676, #1-9 Due Monday

• LO:– Explain the 3 Laws of

Thermodynamics as they relate to conservation of energy

• SC:– Assess experimentally the final

temperature when two liquids of different temperatures are mixed

– Assess experimentally the final temperature when a hot metal is added to cold water

– Calculate the heat lost and heat gained of two objects after they are placed in thermal contact

– Discover if energy is conserved when two objects are placed in thermal contact and reach equilibrium temperature

– Explain the concept of entropy as it relate to objects placed in thermal contact.

• Do Now:– Write LO and SC

on new left side page

– WDYS/WDYT: pg 664

• Agenda:– Do Now– Investigate– Summary

Investigate #1-3• #1-set up data table• #2-3 Create a data table in your

notebook to record all data.• Complete #1-3 in lab.• #3 b-c Construct graph and use to

answer questions

Investigate #4-5• Plan experiment, check procedures

with teacher.• Conduct experiment

Investigate #6• Read Physics Talk, Specific Heat, pg

666-67• Complete #6 a-c

Summary• Discuss how this experiment proves

the law of conservation of energy.

HW: 6.7 PTG, pg. 676, #1-9• LO:

– Explain the 3 Laws of Thermodynamics as they relate to conservation of energy

• SC:– Assess experimentally the final

temperature when two liquids of different temperatures are mixed

– Assess experimentally the final temperature when a hot metal is added to cold water

– Calculate the heat lost and heat gained of two objects after they are placed in thermal contact

– Discover if energy is conserved when two objects are placed in thermal contact and reach equilibrium temperature

– Explain the concept of entropy as it relate to objects placed in thermal contact.

• Do Now:– What does

Conservation of Energy mean to you? Explain your answer

• Agenda:– Do Now– Physics Talk– Practice Problems– Summary

Physics Talk• What did you observe

in your experiment?• Equal amounts of hot

and cold water produced a final temp half way between the initial temps of both

• When you changed the amounts of hot or cold water the final temp was somewhere between the two initial temps, but closer to the temp of the water with the larger mass.

Physics Talk• What is the Law of

Conservation of Energy?

• The total energy in a system is conserved, energy can neither be created or destroyed

• Start=End• The cold water gained

thermal energy through the transfer of heat, then the hot water must have lost and equal amount of thermal energy.

Physics Talk• What equation can

we use to show the Law of Conservation of Energy?

Mass of water?1mL=1g50mL=50g

Physics Talk• What is specific

heat?• Energy is

conserved whether the cool water is mixed with hot water or hot metal.

• The heat energy (J) required to raise the temp of mass (1g) for a substance by 1°C.

Physics Talk• What is the

equation for specific heat?

Physics Talk• Sample Problem

Physics Talk• Conservation of

Energy…Again!• Energy is not

created or destroyed!

• It can change from one from to another, but the total amount remains the same in a closed system!

• Example: From GPEKE

Physics Talk• What is the

difference between Temperature, Heat, and Thermal Energy?

• Temperature is the measure of average kinetic energy of molecules.– High Temp--> more

KE

Physics Talk• What is the

difference between Temperature, Heat, and Thermal Energy?

• Heat is the energy transferred from one place to another due to temperature differences.– Transfers from

High heat to low heat

Physics Talk• What is the

difference between Temperature, Heat, and Thermal Energy?

• Thermal energy is a type of energy that results from the motion of atoms (related to temperature)– Increase thermal energy,

increase temperature– Depends on the mass and

temperature of the water– 100g of hot water > 100g

of cold water because of the difference in temp

– A swimming pool with 10,000kg cold water > 1kg hot water due to mass

Physics Talk• What is

thermodynamics?• The study of the

relationships between heat and other forms of energy transformation of one form into another.

• There are 3 laws of thermodynamics.

Physics Talk• Zeroth Law of

Thermodynamics• If 2 objects have

the same temperature as a third object, then the two objects must also have the same temperature.

• If A=C, and B=C, then A=B

Physics Talk• First Law of

Thermo Dynamics• Conservation of energy

related to hot and cold objects.

• Hot Coffee (90°C) + Cold Milk (5°C) Coffee cools (10°C) slightly, Milk warms a lot (75°C)until they are at the same temperature (80°C)

• Could be calculated with the equation if you know the mass of the coffee and milk.

Physics Talk• Second Law of

Thermodynamics• In irreversible

processes, entropy or disorder always increases.

• Time is irreversible• Thermal energy is

transferred from hot objects to cold objects and NEVER goes from cold to hot spontaneously.

Physics Talk• Second Law of

Thermodynamics• Energy is only

transferred from hot objects to cold objects until they reach an equilibrium temperature.

• There is NO SUCH THING AS COLD ENERGY!

Physics Talk• Second Law of

Thermodynamics (con’t)

• Due to Entropy.– Related to the degree

of disorder of molecules.

– Solids are more organized (ordered) than liquids which are more ordered than liquids.

– To go from solidliquidgas the object must gain thermal energy, increasing entropy.

Physics Talk• Example of

Entropy

Checking Up Questions • Pg. 672, #1-4

Vocabulary Boxes• Complete for all vocab words in

Chapter 6, Section 7.

Essential Questions• Pg. 675–What does it mean?–How do you know?–Why should you care?

Physics To Go• 6.7 PTG, pg. 676, #1-9