AIT Physics 1 Honors
Laboratory: Specific Heat and Conservation of Energy
When energy in the form of heat Q is added to a material, the temperature of the material rises. Note that
temperature, in units of degrees Celsius (°C) or Kelvin (K), is a measure of how hot or cold a substance
is, while heat, in units of joules (J) or calories (cal), is a measure of its thermal energy. 1cal = 4.19J.
A measure of the efficiency with which a substance can store this heat energy is known as specific heat
capacity, or simply the specific heat, . The greater the material's specific heat, the more energy must be
added to change its temperature. As an example, the specific heat of water is given as C
4186
J
,
Kg C
which means that 4186 Joules of heat are necessary to raise one kilogram of water one degree Celcius or
Kelvin. Other common specific heat values for various other materials are listed in CJ6 Chapter 12.
The heat necessary to cause a temperature change in a material (not a phase change) is Q
mC T
where C is the specific heat capacity of that material. Normally the change in temperature of the substance
is the difference between its final and initial temperatures T T f Ti
When two bodies having different temperatures come into contact with each other, heat energy is
transferred between the bodies. Take, for example, placing a piece of hot metal into a container of cool
water. From experience we know over time that the metal sample will become cooler, while the water and
its container will become warmer, until an equilibrium temperature is reached. Put another way,
according to the law of energy conservation the total heat energy lost by the metal is the total heat energy
gained by the water and container:
Qlost
Qmetal
Qgained
Qwater Qcontainer
mmCm Tm
mwCw Tw mcCc Tc
In thermodynamics (which we will start in a week) a negative sign would be used on the Qmetal term to
maintain our sign convention for heat; we set the hot side to be negative because energy is leaving the hot
sample. This equation holds true if no heat is exchanged with the surrounding environment and if none of
the materials undergo a phase change.
For this laboratory you can do your analysis like we did in our homework problems. That is, we will set
T Thigher Tlower which will always provide us with a positive number. If you do not have positive
T then you will need to make the Qmetal term negative.
To isolate this experiment from the environment we will utilize a calorimeter. Our calorimeter is an
aluminum can enclosed by insulation within another metal container acting as a heat insulator.
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OBJECTIVES
With your metal sample, use the calorimeter and determine the specific heat, C m , of the metal
sample and ascertain the identity of the metal sample. Note that the calorimeter cup is made of
aluminum.
Use density arguments to verify the identity of your metal sample.
Account for differences from theoretical expectations
MATERIALS
Computers
Vernier computer interface
Logger Pro
one Vernier Temperature Probe
Calorimeter canister
Mystery metal cube
PROCEDURE
We are going to determine the specific heat of a block of metal. This has already been done many times, so
the value is available in reference books. We will pretend that is not the case!
-If you do not wear glasses please put on a pair of safety glasses for this lab.
1. Obtain a sample metal cube from your teacher. Use the vernier calipers to measure and record the
dimensions of the block. You will use this information to double check the type of material you determine
(from the specific heat measurement) in the lab.
2. Measure (and record to the nearest 0.1 g) the mass of the metal block (on the mass scale in the back of
our lab area) and the aluminum calorimeter cup (slide it out of the calorimeter container).
3. Connect the temperature sensor probe to channel 1 to the LoggerPro interface box.
4. Add exactly 100mL (100mg or 0.1Kg, you will determine the exact mass of water below) of tap water to
the inside cup of the calorimeter. You can bring the inside cup or whole calorimeter to the front sink area.
Measure out 100mL from a Pyrex beaker and pour into your calorimer Aluminum inner cup. Now take the
aluminum calorimeter cup with the cool water in it to the mass scale and record the mass (this is the mass
of the water plus the mass of the aluminum calorimeter cup, you will need to subtract the aluminum
calorimeter cup mass to get an exact mass of the water).
5. Open the LoggerPro program and make sure the temperature probe is recognized by the hardware and
software. You should see a temperature reading at the top left for room temperature (approx 21-23 deg C)
after 10-30 seconds (after the temperature probe has stabilized). Go to the “Experiment” menu and click on
“Extend Collection” until it is greater than 600 seconds (10 minutes). You can make it higher if you want.
This will allow enough time for the temperature to stabilize after you drop the hot metal into the
calorimeter water.
6. Push the Temperature Probe through the hole in the cap so that the end of the probe will be submerged in
the water when the cap is on the canister. Do not let the end of the probe rest against the bottom of the
canister.
7. Return your metal cube to your teacher. We will place the metal cube into an open beaker filled with
boiling water and allow it to sit. We allow it to sit until all of the metal is the same temperature as the
boiling water. We know that the temperature of boiling water is 100.00 °C (assume for your calculations a
Physics 1
Thermal Physics: Specific Heat
temperature of 98 °C since it will drop a degree or two by the time we drop it into the calorimeter (a source
of error to be discussed?)
When you are ready to add the metal mass to your calorimeter, let me know and I will bring the hot metal
cube over to your lab bench to put into your calorimeter.
Alternately I will ask you to record the current water temperature and then bring your calorimeter
over to the front bench where we will put the hot metal cube into the calorimeter. We will assume
that the water temperature will not change in walking from the bench area to the front of the room.
Now we will have to perform a key step.
Click
to begin data collection.
Have one person from you lab group lift the lid off the calorimeter enough to be able to get the metal cube
in but not enough that the temperature probe leaves the water
As quickly as possible, we will pull the metal out of the boiling water and transfer it into the calorimeter
and put the lid and temperature probe assembly back on top.
The hot metal cools down and the water heats up, until the metal cube, the water and aluminum calorimeter
cup get to the same ending temperature. We record this with the LoggerPro graph as the temperature where
the temperature vs. time graph has a slope of approximately 0 (horizontal). Use the Loggerpro software
data analysis tools to record this temperature.
You should also print or save your temperature graph for inclusion in your formal lab report.
At this point we will make a key assumption which will make our task easier. That is to assume that all the
heat lost by the metal winds up in the water. In reality this is not the case. In an actual experiment, the heat
transfer will not be 100% and you have to take steps to compensate for those losses. For this laboratory we
will ignore these losses (you may want to discuss in your Error Analysis).
NOTES:
Caution!!! The metal samples are quite likely to be very hot. Handle with care.
This lab could prove very frustrating and may have to be repeated several times if you do not think through
the steps ahead of time. Carefully plan your experimental procedure. Also, perform all your calculations in
the lab room before you head home.
The precision of the temperature probe is given as ±0.2°C at 0°C, and ±0.5°C at 100°C.
When using the Logger Pro software, you can easily examine the value of each data point with your mouse
by selecting Analyze and then Examine from the software's menu bar.
You may wish to include a screen shot image of the temperature measurements in your lab writeup. To do
so, with the image on the screen, press the Print Screen button on the keyboard. This will place the screen
shot image into memory. For best results, save the image in the GIF format. The image can then be
inserted into your word document.
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DATA TABLE (YOU DECIDE AND RECORD NECESSARY DATA)
TBD
ANALYSIS
1. Calculate the specific heat C for your metal using the heat lost = heat gained equation.
2. Identify your metals using the reference table in your textbook.
3. In which direction, (i.e. from, which) object did heat flow when
i. the metal cube was placed in the boiling water?
ii. the cube was placed in the cool water?
4. What is thermal equilibrium? How can you recognize when thermal equilibrium has been reached?
5. Why was the cube left in the boiling water for 5 minutes?
6. What quantities are needed to be measured in this Objective?
7. Which equation(s) will you use for this Objective?
8. What is the uncertainty of the temperature of the hot water bath? Remember, the hot water bath
temperature is measured with the glass thermometer.
9. How is the initial temperature of the metal samples measured? What steps did you take to insure that this
is a valid measurement?
10. How will you reduce the experimental error when transferring the hot metal sample to the calorimeter?
11. How will you know when to stop taking data for this Objective?
12. If the thermometer or temperature probe touches the metal sample or metal container, how will this
affect the temperature measurements, if at all?
13. How is
determined for each material in this Objective?
14. Discuss various sources of uncertainty in the
measurements?
15. What material did you determine your group has been given for this lab
Additional Questions (answer and include in your formal lab report)
1. In general (in terms of specific heat) what type of materials are good choices for storing solar heat
energy captured by solar cells? Why?
2. Use the fact that C w (the specific heat of water) is large to help explain the role that oceans play on
the world's climate.
3. Why are pots used for cooking often made of copper bottoms with aluminum sides? You may need
to consider the metals' specific heats, densities and price per pound.
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