Heat of Fusion Lab
v5
Dr. Breinan
Chemistry
p.1
Molar Heat of Fusion of Ice
The amount of energy required to convert a solid to a liquid, at constant temperature and
pressure depends on the amount of substance present. However, the amount of heat needed to
melt a specific amount, known as the heat of fusion, is always the same. It is often useful to
refer to the amount of heat needed per gram or per mole of substance. The latter value is called
the molar heat of fusion. The molar heat of fusion is therefore the energy needed to change one
mole of a solid into liquid at the melting point and is specific to that substance. The involvement
of energy can be shown in equation form as follows:
H2O (s) + molar heat of fusion  H2O (l)
You will perform an experiment to determine the molar heat of fusion of ice. An excess amount
of ice will be placed in a calorimeter (styrofoam cup) with a known amount of hot water. You
will allow enough ice to melt to bring the temperature of the ice water to the melting point of ice,
approximately 0°C. At this time the extra ice will be removed. The volume of the melted ice
and water in the cup will be used with temperature data for the calorimeter to calculate the molar
heat of fusion of ice. The density of water (1 g/mL) will be used to convert volume to mass
where needed.
Objectives:
- To determine the molar heat of fusion of ice.
Pre-lab: Complete on a separate sheet.
1. Prepare a data table for this lab. (Hint only 4 values are recorded)
2. Sketch what is in the main styrofoam cup after each of these steps: 1,4,5,7
Do not worry about the thermometer.
3. How will you know how much ice melted?
4. What equation can be used to determine the heat lost by water?
5. What is the specific heat of water? give two values; one using cal, and one using J:
SAFETY: Wear goggles, gloves, and aprons when working with hot water.
Materials:
large styrofoam cup
100 mL graduated cylinder
ice, 5 cubes
600 mL beaker
150 mL beaker
test tube holder
hot water (from thermos or hot plate)
thermometer
scoop spatula
Procedure: Your data will be an important part of your grade! Be prepared! The steps after
step 2 need to be performed without significant delays between steps. Know what you are
doing (see figure 1)! Make sure you can operate your test tube holder easily before starting.
1. Place a large dry styrofoam cup into a 600 mL beaker for support. Have all your equipment
ready including your ice cubes in a separate styrofoam cup.
2. In the 150 mL beaker, obtain about 100 mL of hot water at 70°C or a little higher. You will
either pour the water from a hot source (CAREFUL!), or heat the water yourself on a hot
plate. Do NOT record this temperature or volume!
3. From the 150 mL beaker, pour about 90 mL of hot water into the graduated cylinder. Record
the exact volume. If the water is above 60ºC, let it air cool to 60°C in the graduated
cylinder. Do NOT record this temperature!
Heat of Fusion Lab
Dr. Breinan
v5
Chemistry
p.2
add
ice
hot
water
100 mL
70 °C
about
90 mL
55-60°C
record lowest
temperature,
remove ice
find
volume
4. Pour the water into the styrofoam cup. Rest the thermometer in the cup. The water should be
between 55°C and 60ºC. If it cooled to below 50°C go back to step 2.
5. Record the exact temperature of the water and immediately add 5 full-size (6 if a bit smaller)
ice cubes to the cup. Make sure you add only ice, not water. Also be careful not to splash!
6. Stir constantly and monitor the temperature in the middle of the water near the floating ice (not
on the bottom). Watch the temperature go down and observe that the ice is melting. You are
waiting until the temperature of the ice and water pretty much stops going down...meaning it
takes about 15 seconds to drop by 1ºC usually somewhere between 0 and 5°C, depending on
your thermometer. [** You must keep the ice from all or mostly all melting during this step!
If your ice pieces are getting too small (small grape size), add one or two more ice cubes! IT
IS OK to add more ice at this time!] RECORD the low (final) temperature and go quickly
to step 7. It is better to stop a bit early than to wait too long before step 7.
7. Remove the remaining ice from the water as quickly as possible without losing any of the
water. It is usually best done with a test tube holder. A spatula may also help for very small
pieces.
8. Carefully determine the final volume of the cold water in the styrofoam cup by pouring it back
into a graduated cylinder and measuring (CAREFUL: don’t overflow the graduated cylinder!)
If you encounter any difficulties, figure out how to do this. Record this volume.
9. Write your data on the board.
10. Clean-up / disposal... leave your equipment to dry on the rack.
11. Start to calculate the heat of fusion.
Processing: Present your data, perform calculations and answer questions neatly on a separate sheet.
(see sample calculation for hints). Even though the steps are laid out for you, you MUST practice
explaining clearly what you are doing in each step! Pretend your only instruction was to “calculate the
heat of fusion.” Multi-step calculations such as this must be clear and easy to follow! Remember to
use sig figs!
1. Calculate the change in temperature of the original hot water in the calorimeter.
2. Calculate the heat lost by this water in calories and joules.
3. Calculate the heat used to melt the ice.
4. Calculate the volume of ice melted.
5. Calculate the mass of ice melted.
6. Calculate the moles of ice melted.
7. Calculate the heat of fusion in the following units: cal/g cal/mol
kJ/mol
Questions:
8. Which values from #7 above represent the molar heat of fusion?
9. What was your percent error? (Be sure to get or look up the accepted value to 3 SF)
Heat of Fusion Lab
v5
Dr. Breinan
Chemistry
p.3
10. If you repeated the experiment with 10 mL less hot water, how would the molar heat of fusion be
expected to differ (higher, lower, or the same?) Explain.
11. What assumptions did you make about the temperature of the ice before and after it melted?
12. If heat was lost from your calorimeter (styrofoam cup) while the ice was melting, would it have
made the value for the molar heat of fusion that you calculated higher or lower than the accepted
value? Explain clearly.
13. What other sources of error were present in this experiment? Specifically, how could they affect
your result?
Extra Credit: Calculate the heat of fusion of ice if the ice you were given was originally at -10°C. Hint:
the specific heat of ice is 0.5 cal/g°C. Hint 2: what assumption must change? Explain your approach
clearly!
Sample calculation:
Volume of hot water: 90.4 mL
Temperature of hot water: 53.6°C
Final minimum temp (water and ice): 0.7°C
Volume (hot water + melted ice): 151.9 mL
1. Calculate the change in temperature of the original hot water in the calorimeter:
The water cooled from 53.6°C to 0.7°C. T = 53.6°C - 0.7°C = 52.9°C
2. Calculate the heat lost by this water (Qw) in calories and joules:
Since the density of water is 1g/mL, the mass of 90.4 mL of hot water is 90.4 g
Qw=mw•c•T = (90.4 g)(1.00 cal/g°C)(52.9°C) = 4780 cal
(use 4.184 J = 1 cal to convert)
3. Calculate the heat used to melt the ice (Qi). Assume that all of the heat lost by the water went into
melting the ice. Therefore, Qi=Qw= 4780 cal
4. Calculate the volume of water that is from ice melted. The difference between the final volume and
initial volume is due to melted ice. Vi = 151.9 mL - 90.4 mL = 61.5 mL.
5. Calculate the mass of ice melted. The melted ice is now water. Use the volume you just calculated.
With a density of 1 g/mL, 61.5 mL = 61.5 g
6. Calculate the moles of ice melted. Use the molar mass to convert. Ice is simply H2O
61.5 g 1 mole ice

 3.42 mol
1
18.0 g
7. Calculate the heat of fusion. For example, in cal/g. Values with other units may be calculated
similarly, or may be obtained by converting the units in this answer.:
Heat of fusion =
Heat to melt ice
Qi
4782 cal


= 77.8 cal/g
g or moles ice
g or moles
61.5 g
Practice: Not required for this lab, but will help in studying if Dr. B tells you that the lab calculation will
be on an upcoming quiz or test:
120.5 mL of water are measured in a graduated cylinder and are placed in a styrofoam cup. The
temperature of the water is found to be 40.2°C and some ice is immediately added. The ice water is
stirred until the temperature reaches a minimum temperature of 1.7°C. The excess ice is quickly
removed. The remaining water is poured into graduated cylinders and measures 182.2 mL. Based on this
data, calculate the heat of fusion of ice in cal/g and in kJ/mol.
Answers: 75.2 cal/g and 5.66 kJ/mol