Download Specific heat

Do Now
Thursday, January 09, 2014
You heat a balloon filled
with air. What happens to
the pressure inside of the
balloon? Why?
3.5 minutes
Do Now Check
By the end of the day
today, IWBAT…
• Explain and calculate
specific heat
Why it matters in LIFE:
Explains why certain
objects are made out of
certain materials
Why it matters in THIS
CLASS: This is the last topic
we are covering before
spring break – you will have
a mastery quiz on Monday
so let’s hit 85%!
Agenda
Do Now
5 min
Thermometer Lab Wrap Up
5 min
Specific Heat C-Notes
10 min
Specific Heat Practice Problems 30 min
Thursday, 01/09/14
TEKS:
P.6E: Describe how the macroscopic
properties of a thermodynamic
system such as temperature, specific
heat, and pressure are related to
the molecular level of matter,
including kinetic or potential energy
of atoms
By the end of today,
IWBAT…
Explain and calculate
specific heat
Essential Question:
What is specific
heat?
Topic:
Specific Heat
Thermometer Lab Wrap Up
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What were the two systems you dealt with in this lab?
Which system is transferring energy into the water? How do you
know?
After you turned the hot plate on, what happened to the molecules
on the surface of the plate?
What type of energy is being transferred from the hot plate to the
water?
How does this transfer of energy affect the molecules of water?
How does this transfer of energy affect the molecules of the liquid
inside the thermometer?
As particles of water strike the thermometer and transfer their
energy into the liquid inside, what happens to the pressure of the
thermometer’s liquid?
How does this change in pressure allow us to use a thermometer
to measure the temperature of a system?
Specific Heat
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In the last step of your lab, you calculated the total
heat that was put into your system in order to raise
the temperature of the water
In order to be able to do this, you needed to know
the SPECIFIC HEAT of the water
Specific Heat
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Specific heat is a property of matter that describes
the amount of energy required to raise the
temperature of one gram of a substance by 1 °C
Specific Heat
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Specific heat is a constant that relates heat and
temperature change per kilogram
Different materials have a different specific heat
A low specific heat means heat is conducted through
an object quickly
Specific Heat
CONDUCTORS: change heat easily
Low Specific Heat
Require little energy to change temp
INSULATORS: Do NOT change heat easily
High Specific Heat
Require LOTS of energy to change temp
Material
C
Water
4184
Plastic Foam
2010
Air, 200 K
1650
Aluminum
897
Iron
449
Brass
375
Conductors
Insulators
Specific Heat
Recall the “Fire Proof Balloon”
Specific Heat Demonstration
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We have two balloons – one filled with water and
one filled with air
Based on what you
learned yesterday
about temperature and
pressure, what actually
happens to the balloon?
Specific Heat – Equation
Q = mCDT
Q = mC(Tf – Ti)
Q = heat (joules-J)
m = mass (kg)
C = specific heat (J/kg C)
DT = change in temp (C)
Specific Heat Demo
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Why did the balloon filled with water not explode?
The water balloon does not explode because the
water inside absorbs the heat better than the air
does
Water has a HIGHER specific heat, which means it
has a HIGH heat capacity
 It
takes a lot more energy to change the temperature
of the water than it does for the air
Practice Problem - Q = mCDT
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If the specific heat of methanol is 251 J/kg˚C, how
many Joules of heat are needed to raise the temp
of .250 kg of methanol from 18˚C to 33˚C?
Group Practice
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A .625 sample of water was cooled from 50˚C to
10˚C. How much heat was lost? The specific heat of
water is 4,184 J/kg˚C.
Group Practice
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The heat capacity of lead is 130 J/kg˚C. How
much heat (in J) is required to raise the temperature
of 15 g of lead from 22˚C to 37˚C?
Group Practice
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What is the specific heat of a substance that
absorbs 250 J of heat when a sample of 10 kg of
the substance increases in temperature from 10˚C to
70˚C?
Exit Ticket
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Complete the exit ticket questions INDEPENDENTLY
You are not getting enough INDIVIDUAL practice
before assessments, which is one of the reasons why
the grades are so low
You don’t really know it unless you can do it ON
YOUR OWN