E-8
HEATS OF SOLIDIFICATION & COMBUSTION LAB
NGSS: HS: PS3-1 Create a computational model to calculate the change in the energy of one
component in a system when the change in energy of the other component(s) and energy flows in
and out of the system are known. PS3-4 Plan and conduct an investigation to provide evidence that
the transfer of thermal energy when two components of different temperature are combined
within a closed system results in a more uniform energy distribution among the components in the
system (second law of thermodynamics). CC Systems and System Models. SEP Planning and
Carrying Out Investigations. SEP Obtaining, Evaluating, and Communicating Information. SEP
Analyzing and Interpreting Data. SEP Engaging in Argument from Evidence. SEP Using
Mathematical and Computational Thinking.
As you have learned in E-3 “Types of Observations” and E-7 “Physical and Chemical Changes”, there
are four indicators of a chemical change. One of those indicators of a chemical change is a change in heat
or energy. Combustion (burning) is an example of such a chemical change. We may also simply apply or
take away heat from an object directly to cause it to undergo a physical change of state. Liquefaction
(melting) and solidification (freezing) are examples of such physical changes.
To calculate the heat of solidification and the heat of combustion, we must use the following equation:
Heat (in Joules) = specific heat of water  mass of water heated  change in temperature of water.
Note: the specific heat of water is 1.00 cal/g °C or 4.18 J/g °C. In this experiment, we will be using the
specific heat value of that is given in Joules, since that is the current SI unit for Energy.
To calculate the heat per gram of material solidified or combusted, we then simply take heat in Joules
and divide it by the mass of material solidified or combusted.
Is there a difference in the amount of heat change per gram in a chemical and in a physical change? In
this lab, we shall see!
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Purpose:
1. To give the formula used for calculating heat in Joules.
2. To determine which process, solidification or combustion, is a chemical change and which is a
physical change.
3. To list the heat in Joules per gram produced by the physical change and the chemical change in the
E-8 lab and conclude which kind of change produces more heat (Make sure to use correct significant
figures and labels!).
4. To list two possible sources of error in the E-8 lab and explain how they would affect the results of
the lab.
Materials:
Part 1 ring stand
Bunsen Burner
test tube with wax
small thermometer
ring
400 mL beaker
Styrofoam cup
100 mL graduated cylinder
wire gauze
tap water
test tube holder
matches or lighter
ring
large can
tap water
100 mL graduated cylinder
small juice can
tin can lid
matches or lighter
Part 2
ring stand
glass stirring rod
candle
small thermometer
Safety Alerts: Goggles, tie back hair, close fitting sleeves, long pants, closed toed shoes/ heat,
vapors, hot wax, glass.
1
Day 1 – Heat of Solidification (melting)
Procedure:
1.
Obtain a large test tube containing solid wax. Carefully place the test tube on an electronic balance and
mass the test tube to the nearest 0.01 g. Record the mass of the full test tube in grams in your data table.
2.
On the test tube, a mass will be written. This is the mass of the empty test tube. Record the mass of the
empty test tube in grams in your data table.
3.
Calculate the mass of the wax to be solidified (melted). To do this, subtract the mass of the empty test
tube from the mass of the full test tube. Record the mass of the wax to be solidified (melted) in grams in
your data table.
4.
Attach a ring to a ring stand. Place a piece of wire gauze on the ring. Place a beaker approximately 2/3
full of tap water onto the wire gauze. Light a Bunsen burner and adjust it to produce a moderate size
flame with an inner blue cone. Place the Bunsen burner under the wire gauze. The flame tip should be
directly under the wire gauze. If it is not, adjust the ring.
5.
Carefully lower the test tube containing the solid wax into the beaker so that it is near, but not touching,
the bottom of the beaker. Wait until all of the wax is completely melted. When this happens, extinguish
the Bunsen burner flame.
6.
While you are waiting for the wax to melt, obtain a Styrofoam cup. Fill the cup with enough tap water to
cover the height of the wax in the test tube. Using a small thermometer, record the temperature of the
water in the Styrofoam cup (This is the temperature of the water before.). Record the temperature of the
water in the Styrofoam cup before to the nearest 0.5 degree Celsius in your data table.
7.
Once the wax in the test tube is melted, use a test tube clamp to carefully remove the test tube from the
400 mL beaker. DO NOT tip the test tube! Hold it in air until you see the first trace of solid appear in
the test tube. When solid appears, lower the test tube into the Styrofoam cup. Do not let the test tube
touch the bottom or sides of the cup! Use the test tube clamp to swirl the test tube gently around in the
cup until the exact point at which all of the wax is solidified. Using a small thermometer, record the
temperature of the water in the Styrofoam cup (This is the temperature of the water after.). Record the
temperature of the water in the Styrofoam cup after to the nearest 0.5 degree Celsius in your data table.
8.
Calculate the change in temperature of the water. To do this, subtract the temperature of the water before
from the temperature of the water after. Record the change in temperature of the water in degrees
Celsius your data table.
9.
Pour the water from the Styrofoam cup into a 100 mL graduated cylinder. If you have more than 100 mL
of water, add the two volumes of water to get the total volume. Record the volume of water used to the
nearest 0.5 mL in your data table. Note: Because the density of water is 1.00 g/mL, you have just
found the mass of water as well!
10. Clean up and put all materials used back in their proper place.
Data Table:
mass of the full test tube
mass of the empty test tube
mass of the wax solidified (melted)
temperature of the water in the
Styrofoam cup before
temperature of the water in the
Styrofoam cup after
change in temperature of the water
2
volume/mass of the water used
3
Day 2 – Heat of Combustion (burning)
Procedure:
1.
Obtain a candle and tin can lid. Mass the candle and lid on an electronic balance to the nearest 0.01g
(This is the mass of the lid and candle before.). Record the mass of the lid and candle before in
grams in your data table.
2.
Set up a ring stand with ring. Obtain a small juice can. Thread a glass stirring rod through the two
holes in the small juice can. Place the juice can on the ring so that the can swings freely in the center
of the ring. Place the candle and tin can lid on the base of the ring stand directly below the small
juice can. Place a large can around the candle. Lower the ring as far as possible (Make sure there
will be place for the candle flame, when lit!).
3.
Remove the small juice can from the set-up and fill half full with tap water. Measure the
temperature of the water using a small thermometer (This is the temperature of the water before.).
Record the temperature of the water in the juice can before to the nearest 0.5 degree Celsius in your
data table.
4.
Remove the large can from the set-up. Using a match or lighter, light the candle. Replace first the
large can and then the small juice can. Stir the water in the small juice can gently with the small
thermometer. Heat the water until it is 15-20 °C above room temperature. Measure the temperature
of the water again with the small thermometer (This is the temperature of the water after.). Record
the temperature of the water in the juice can after to the nearest 0.5 degree Celsius in your data
table.
5.
Calculate the change in temperature of the water. To do this, subtract the temperature of the water
before from the temperature of the water after. Record the change in temperature of the water in
degrees Celsius in your data table.
6.
Pour the water from the small juice can into a 100-mL graduated cylinder. If you have more than
100 mL of water, add the two volumes of water to get the total volume. Record the volume of water
used to the nearest 0.5 mL in your data table. Note: Since the density of water is 1.00 g/mL, this is
also the mass of water.
7.
Remass the candle and lid on an electronic balance to the nearest 0.01g (This is the mass of the lid
and candle after.). Record the mass of the lid and candle after in grams in your data table.
8.
Calculate the mass of the candle wax combusted (burned). To do this, subtract the mass of the lid
and candle after from the mass of the lid and candle before. Record the mass of the candle wax
combusted (burned) in your data table.
9.
Clean up and put all materials used back in their proper place.
Data Table:
mass of the lid and candle before
mass of the lid and candle after
mass of the candle wax combusted
(burned)
temperature of the water before
temperature of the water after
change in temperature of the water
volume/mass of the water used
4
Calculations: Show all your work!!!! Make sure to give your answer with correct labels and
number of significant figures!
Day 1
1. Calculate the heat of solidification (freezing) in Joules. Use this equation:
Heat in Joules = specific heat of water  mass of water used  change in temperature of
water. The specific heat of water is 4.18 J/g °C. Plug this value into the equation above
2. Now, calculate the heat of solidification in Joules per gram of wax solidified. Take the heat in
Joules (from #1) and divide it by the mass in grams of wax solidified (from your data table).
Day 2
3. Calculate the heat of combustion (burning) in Joules. Use the same equation as in Day 1 #1:
Plug the Day Two values into the equation above.
4. Now, calculate the heat of combustion in Joules per gram of wax combusted. Take the heat in
Joules (from #3) and divide it by the mass in grams of wax combusted (from your data table).
Write your final answers in the chart:
heat of solidification
heat of solidification per
gram
heat of combustion
heat of combustion per gram
Questions:
1. Why was it better to use a Styrofoam cup in Day 1 than a glass beaker?
2. What was the function of the large can in Day 2?
3. What is the relationship between the volume of water used and the mass of water used in each
part? What relationship makes this so?
4. Compare the heat in Joules per gram of wax solidified and the heat in Joules per gram of wax
combusted. Which produces more heat, solidification or combustion?
5. What kind of a change is solidification (physical or chemical)?
6. What kind of a change is combustion (physical or chemical)?
7. Which kind of change produces more heat per gram (a physical change or a chemical change)?
8. What was your value for heat of combustion per gram? How many Joules would be produced is
275 g of candle wax were burned?
Conclusion:
5