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Do NowThursday, January 08,
2015
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, 01/08/15TEKS:
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
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
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
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
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
INSULATORS: Do NOT change heat easilyHigh Specific HeatRequire LOTS of energy to change temp
Specific Heat
CONDUCTORS: change heat easily
Low Specific Heat
Require little energy to change temp
Specific Heat
Material C
Water 4184
Plastic Foam 2010
Air, 200 K 1650
Aluminum 897
Iron 449
Brass 375
Insu
lato
rs Con
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Recall the “Fire Proof Balloon”Specific Heat Demonstration
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 = mCDTQ = mC(Tf – Ti)
Q = heat (joules-J)m = mass (kg)
C = specific heat (J/kg °C)DT = change in temp (°C)
Specific Heat Demo
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 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
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
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
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
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