There are three phases of matter: solid, liquid, and gas. When substances are changing phase, temperature remains constant. Since temperature is a measure of average kinetic energy, during phase change there is a change in potential energy and not kinetic energy.
In order for a substance to melt or to boil, external energy must be added; the potential energy of the substance will increase by the absorption (taken on) of this externally applied energy. When the two types of condensation occur (liquefaction or freezing) the reverse to the above occurs. Energy is released (given off) upon the phase change and a subsequent decrease in potential energy occurs.
In our experiment, wax solidifies and gives off heat. This heat is gained by the water causing the temperature of the water to increase. Since we will assume no heat is lost, we can say that:
Heat lost = Heat gained
H lost by wax in tube = H gained by water in Styrofoam cup
H = mH s
H=mc

T
H = heat (calories) m = mass (grams)
 T = change in temperature (ºC) [T
2
– T
1
] c = specific heat (calories/gºC) [c for water = 4.18 J/gºC]
Heat of fusion (H f
) = Heat of solidification (H s
)
(J/g) (J/g)
S
H
H f s
L
 hot plate

250 mL beaker (test tube support)

400 mL beaker (cup support)

600 mL beaker (to heat water)
 test tube holder
 electronic balance
 triple beam balance

TI-83 / CBL or LabPro / Temperature Probe
 large test tube containing wax (paraffin)

Styrofoam cup
Melted wax can cause burns. Wear safety goggles and apron.
Start heating about 300 mL of tap water in a 600 mL beaker to a near boil.
1 first sign of cloudiness

Part 1: mc

T
1. Weigh the test tube filled with wax on the electronic balance. Record the mass (use this value for both trials).
2. The mass of the empty test tube is given on the tube. Record this value.
3. On a triple beam balance, weigh an empty and dry Styrofoam cup and record it in your data table. Be sure to use the same triple beam balance for both trials.
4. Add about 100 mL of tap water to the Styrofoam cup. Record the weight of the water and cup in your data table. Set the
Styrofoam cup of water into a 600 mL beaker (support) and set aside for future use.
Part 2: mH s
5. Prepare the computer using LoggerPro and LabPro:
LabPro Instructions
1. Plug the Temperature Probe into Channel 1 of the LabPro. Use the link cable to connect the computer to the
LabPro.
2. Open the Vernier Software file in programs and select Logger
Pro
3. Set up Logger Pro for data collection. a.
Select the Data Collection operation from the task bar. b.
Select Time Based collection for 600 second. Set 10 seconds between each sample collected. c.
Press Done. a.
Do not begin data collection yet!
6. Place the temperature probe into the water in the Styrofoam cup from Part 1.
7. To melt the wax, place the sold wax test tube in the hot water beaker.
8. Use a test tube holder to remove the tube from the hot water bath and carefully wait for it to cool, looking at the bottom of the test tube for the first signs (i.e. cloudiness) of solidification to occur. Wipe extra water off the outside of the test tube.
9. When the first sign of cloudiness is observed, begin collecting data by selecting the green right arrow button in the Logger Pro toolbar.
10. Immediately place the test tube of wax in the Styrofoam cup. At no time is the temperature probe to be put into the wax.
11. Stir the water using the temperature probe as data is being collected.
12. When finished collecting data, move the cursor along the graph using the arrow keys or the mouse. Record data points of the initial temperature and the highest temperature to the nearest 0.1ºC.
13. For the second trial, empty and dry your Styrofoam cup. Find the mass of the empty, dry cup and the cup with 100 mL of tap water as you did for the first trial. Keep test tube upright and do not reweigh.
14. Repeat for an additional 2 trials.
Return all equipment and materials to the proper area for storage.
Make a data table like the one below in your lab notebook. Be sure to include a relevant title for the table and units in the column headings.
Mass of wax (use the electronic balance and the same value for both trials) mass of the empty test tube mass of the test tube and wax mass of the wax
2

Mass of water (use the same triple beam balance for both trials)
Trial 1 mass of empty cup mass of cup and water mass of water
(done for both trials) initial temperature of water final (highest) temperature of water change in temperature
Trial 2
Calculate the Heat of Solidification (H s
) of paraffin for each trial and then find the average Heat of Solidification.
Heat lost = Heat gained
H lost by wax in tube = H gained by water in Styrofoam cup
H = m wax
H s
H=m water c

T
In writing this section, keep in mind your audience is not your instructor. It is someone at your level who has not performed the lab. You should write your data analysis section with not only your work, but a clear description of how you arrived at your answer including the original formula for your calculation and a description of the variables in the formula.
This section should involve a three paragraph journal entry.
Paragraph 1: Draw a conclusion to your work by stating what you did in the lab in 1-2 sentences followed by your experimental value for the heat of solidification of paraffin. Compare this value to the excepted value for the heat of solidification of paraffin- 150 J/g- using a percent error calculation.
Paragraph 2: Discuss possible sources of error in the lab that could used to explain why your value is different from the theoretical value. Only include experimental design error, not statements such as, “I didn’t measure carefully,” or “The balance read the mass wrong.”
Paragraph 3: Describe possible solutions or changes that could be implemented if you were to perform the lab again that could correct or lessen the error you experienced.
3