Chapter 6, Section 7
Laws of Thermodynamics:
Too Hot, Too Cold, Just Right
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:
– Write LO and SC on new left side
page
– WDYS/WDYT: pg 664
• Agenda:
– Do Now
– Investigate
– Summary
Investigate #1-3
• #1-complete in your notebook
• #2-3 Create a data table in your notebook
to record all data.
• #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 66667
• 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=1g
50mL=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
GPEKE
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
solidliquidgas 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