Lab – Determining the Heat of Fusion for Ice
Introduction and Background:
As we know to increase the temperature of water it takes heat energy and this is given by the formula Q = mCT. Meaning
that the temperature increase is directly proportional to the heat put into the system; however, this is not the case during a
PHASE CHANGE (i.e. melting, freezing, boiling, etc.).
During a phase change the temperature of the substance remains CONSTANT!! This is due to the fact that the energy
being put into the system is being used to break the intermolecular forces between the molecules allowing them to separate
causing the phase change. This is shown graphically below.
This means that we can no longer use the formula Q = mCT to determine the amount of heat put into the system since
there is NO temperature change during the phase change meaning this formula would produce an answer of zero which is
incorrect. Therefore we introduce the concept of Latent Heat for phase changes.
Melting/Freezing  Latent Heat of Fusion (Hf) = The amount of energy taken from the surroundings (or given to) to melt
(or freeze) 1 g of the sample in the system.
Boiling/Condensing  Latent Heat of Vaporization (Hv) = The amount of energy taken from the surroundings (or given to)
to vaporize (or condense) 1 g of the sample in the system.
For a PHASE CHANGE  Heat = (Mass of sample change) × (Latent Heat)  Q = m H
Note: The units of H are (J/g)
Note: Looking at the diagram above if you were to bring this system from 40 C to 80 C there would be THREE DISTINCT
AREAS OF HEAT GAINED BY THE SYSTEM.
1. To heat system from 40 C – 70C (which is the melting point) Q = m c T
2. To melt the system Q = m H
3. To heat the system from 70 – 80 C Q = m c T
BE VERY CAREFUL WITH THIS TO COMPLETE THE LAB BELOW SINCE YOU ARE NOT ONLY MELTING THE ICE
(THE SYSTEM) BUT YOU ARE ALSO HEATING IT UP TO REACH THERMAL EQUILIBRIUM WITH THE WATER.
Lab – Determining the Latent Heat of Fusion for Ice
Materials:
Calorimeter (Styrofoam cup in a 400 mL beaker with a cardboard cup lid), Lab Quest with temperature probe, Graduated
cylinder, ice
Method:
1) Obtain a Styrofoam cup, cardboard lid, Lab quest with temperature probe
2) Measure the mass of an empty Styrofoam cup. Record,
3) Using the graduated cylinder add 70 mL of hot tap water to the Calorimeter. Measure the mass of the Styrofoam
cup and water. Record.
4) Take the initial temperature of the water. Record.
5) Obtain a small amount of free melting ice.
6) Place the ice into the calorimeter. DO NOT touch the ice with your fingers. Dry the ice so that no melt water is
added to the Styrofoam cup. Allow the ice to melt and record the final temperature of the mixture.
7) Measure the mass of water, melted ice and Styrofoam cup. Record. Use this value to determine the amount of ice
that was melted. Record.
8) Repeat this experiment 3 more times using a different amount of ice cubes.
9) Use your results to determine the Latent Heat of Fusion of Ice.
a. Calculate the energy (Q) released from the hot water.
b. Calculate the energy (Q) absorbed by the melt water as it came to the final temp
Energy released by hot water = Energy absorbed to melt ice + Energy absorbed to increase temp of melt water
(m × ΔT × c)
=
(m × Hf)
+
(m ×ΔT × c)
Trial 1
Trial 2
Trial 3
Mass of empty cup
(do each time)
Mass of cup and hot
water
Mass of hot water
only
Initial Temp of hot
water
Final Temp of hot
water w/ melted ice
Change in temp of
hot water
Initial temp of melted
ice-water (Known, not
measured!)
Change in temp of
melted ice water
Mass of cup, hot water
& melted ice water
Mass of ice/melted
water
Specific Heat of
water (known from
notes)
*****Solve for Hf above for each of the three trials on a separate piece of paper.